Imagine all the things that might go wrong with an active 4-year-old along on an 11-day cruise of the Mexican Riviera, and you probably wouldn't risk it.

Unless, that is, you knew that some cruise lines are now making a special effort to attract young families by providing spacious playrooms, supervision practically around-the-clock and special activities to keep kids busy and happy so Mom and Dad can have the freedom to enjoy a real vacation.

With mixed optimism and uncertainty, I boarded Sitmar Cruises' newly launched, 46,314-ton Fairsky in November with my husband and our son, Christopher, to take advantage of what the line had described as the most extensive youth program afloat.

Although up to 350 kids could be expected on a typical summer or holiday cruise, would there be enough playmates during the off season? Could a 4-year-old share our pleasure in being served gourmet meals by candlelight? And what about shore excursions? Was it too much to hope that we could enjoy seeing Acapulco, Zihuatanejo, Puerto Vallarta, Cabo San Lucas and Mazatla'n together -- and still have time to relax without our son and indulge in some real pampering for ourselves?

Among four busloads of passengers en route from Los Angeles airport, there was only one child: ours. No doubt those senior citizens were wondering about us as much as we were about them. But when we saw the 11-story ship, the world's third largest cruise ship, we realized there was more than enough room for the 1,200 passengers sailing this trip (though the Fairsky can carry about 1,700).

Giddy from one discovery after another -- beginning with the hydraulically operated bunk bed that lowered from the ceiling of our spacious cabin -- we left our bottle of champagne unopened on the nightstand and set out to explore the ship. There were six lounges, two dining rooms, a pizza parlor, one theater, a disco, a casino, a gymnasium, an outdoor volleyball court, jogging track, three outdoor pools, three shops, a library and a cardroom. With equal interest I began counting children -- 63 from nine months to 16 years old were aboard, I learned later; at least Christopher would not be alone.

At the Youth Center, four counselors in blue blazers greeted Chris as he headed for the huge split-level climbing apparatus that dominated one of the two large playrooms. There were comfortable tiered sofas, pint-size table-and-chair sets, shelves full of books, and puzzles and action toys. Inside cupboard doors, cuddly toys, trucks, Lego sets and more awaited our son's attention. We had no regrets about packing only a few storybooks and his teddy bear.

For babies there were cribs and swings. Beyond an alcove containing 10 video games was a teen room outfitted with large tables for crafts, games and snacks, plus a giant video screen and VHS. On the large deck outside was a shallow kid's pool with slide and a high net rope fence to guarantee safety. A sign-in system was designed to give the counselors full responsibility for each child's whereabouts. Trusting that it worked was up to us.

The first day at sea stretched endlessly, expectantly, ahead. I made three massage appointments beginning later that morning, then headed for 15 laps on the jogging track. To starboard we were skirting Guadalupe Island, a craggy counterpoint to the vast open sea. I felt strong in the bright, breezy morning air, not my usual tired self.

The massage therapist cut through months of tightness and tension, and it was just a few steps to the whirlpool bath. In one morning I achieved a wondrous sense of freedom.

Armed with four books, my husband chose a deck chair or the plush piano lounge, adjusting his reading selection to his mood of the moment.

Christopher was the only one on a schedule. His Youth Center activity sheet, which arrived nightly in our cabin, foretold the next day's hourly program:

Exercises on deck at 9 a.m., arts and crafts (mobiles today) at 10, a game of follow the leader at 10:30, coloring at 11, Indian art at 11:30. At noon the choice was the buffet on deck, pizza or lunch in the dining room with Mom and Dad. At 1 p.m., swimming; 3, Ping-Pong; 4, an ice-cream party. And so it went -- bingo, TV, trivia, charades, study time and bedtime stories.

Four counselors were always on duty in the Youth Center from 9 in the morning until as late as midnight every day. It became Chris' special niche, his favorite place to be. Naps were postponed and often abandoned as he became ever more attached to his new friends. We'd heard that a child his age has the stamina of an Olympic athlete -- and now he was proving it.

The excellent cuisine was served with flair by adept Italian and Portuguese waiters. We particularly savored the pasta courses, the shellfish and the creamy homemade ice cream.

At dinnertime, we found the best solution was to feed Chris in our cabin, having made selections from menus that were hand-delivered the previous night. Occasionally we dressed him in his blue suit and tie to share the dining-room experience, more for our enjoyment than his. (Early seating was best suited to his schedule.)

Having become accustomed to the ship's routine, we now faced the challenge of our first adventure ashore. Unsure about dealing with taxi drivers in Spanish, we took the morning bus tour of Mazatla'n -- a fishing mecca noted for marlin and sailfish. Luckily we carried a small snack for Chris, who keenly questioned the scenes of this poverty-fringed resort town. While he wasn't tempted to drink the water, ice-cream stands were everywhere and had to be scrupulously avoided.

That afternoon, while my husband napped and Chris played, I couldn't resist the packaged Mexican fiesta we were driven to as part of one of the shore excursions. It was time for a bit of mariachi entertainment with typically dour-faced musicians accompanying the swirling pageant of colors and patterns as the sen oritas spun out their native dances. But the enthusiasm I was seeking at the fiesta, I found at Sen or Frog's, a lively restaurant on Avenida del Mar, the town's main thoroughfare paralleling a wide slash of beach. Mazatla'n was at its most attractive as twilight softened the scene.

After another full day at sea, we docked the following morning at Acapulco for a two-day visit. It was the furthest point of the 3,270-nautical mile, round-trip journey. At dockside, the brightly garbed peddlers were so insistent on displaying their wares that Chris thought they wanted to give us some presents. At La Quebrada Cliffs, he excitedly watched the young men complete a dangerous ascent and then make their 136-foot plunge between massive rocks into the ocean. At the town quay -- where fishermen mend nets for their skiffs and cats laze in the warm sun -- a glass-bottom boat ride struck our fancy.

By lunchtime, Chris was anxious to go back to the playroom, freeing us to taxi past the miles of luxury hotels, parks, boutiques, beaches and a panoramic view of the bay to the Princess Hotel, a fantasyland for grownups with Disney-like pools, sunken bars and waterfalls.

The next morning we all went ashore again by tender and strolled through Acapulco's narrow old town streets buying T-shirts and jewelry. Then, while Chris ate a club sandwich in the playroom, my husband and I lunched at La Concha Beach Club, part of Las Brisas Hotel. Para-sailers glided 350 feet above the bay, as we floated in natural saltwater pools, relaxed and content.

The Fairsky's dazzling departure party from Acapulco Bay, with music, buffet supper and railings ringed with palm fronds, inspired the passengers to participate in sing-alongs and conga lines with abandon.

Of course, the cruise wasn't all fun and games; there were realities to deal with. A self-service laundry room provided 10 washers, dryers and ironing boards -- even an attendant to fold. When Chris developed a cough, there was no medicine aboard in child's portions (luckily, the cough subsided on its own). Seasickness never was a problem. Steam turbine engines, more expensive to operate than the diesel engines many new ships have installed, made for uncommonly smooth sailing; the Pacific Ocean, true to its name, is always less rough than the Caribbean, according to Captain and Fleet Commander Guiseppe Quartini.

On day seven we arrived at Zihuatanejo, a sleepy village whose dusty, unpaved roads are lined with silver shops and boutiques. There was good snorkeling here, but while my husband and Chris went for a swim at the ship-sponsored beach party, I took a 10-minute taxi ride over the mountain to see Ixtapa, a new resort complex carved out of a jungle setting. There are several impressive hotels; however, I was too spoiled by the Fairsky's comforts and mobility to enjoy the humidity and isolation.

The next day, at Puerto Vallarta, the three of us wandered along the shore in the mood for serendipity. There were horses to rent, a perfect way to savor this loveliest of beaches, ringed by high mountains and voluminous clouds. After riding for an hour past curious sunbathers along the resort-lined strand, my husband decided to try the para-sailing. He soared and circled over the sea toward the Fairsky anchored in the distance. (And we thought traveling with a child might tie us down!)

Masquerade night on the ship is an event made for kids. Counselors had materials and time to create a delightful array of pirates, angels, clowns, hula girls, chocolate bars and Keystone cops who paraded into the showroom for introductions and prizes.

Imagination and effort also went into other special children's events: a private tour of the bridge with the Captain, a tour of the ship, a visit by one of the ship's entertainers. Pizza parties, sundae-making and throwing bottle messages overboard were favorite activities.

On the next to the last day, we disembarked at Cabo San Lucas and took Chris on an outboard motorboat ride to Los Archos, the cluster of natural cliffs etched with caves and one perfect arch. Pelicans, seals and waterfowl added their noisy welcome. Then I hurried into town, emerging with a papier-mache' parrot, cotton rug and blanket. It was our final shore excursion.

Time, which had lost real meaning during the cruise, passed quickly the last day at sea. We played another spirited game of Trivial Pursuit with new friends; we pushed the call button one more time for a mid-afternoon fruit basket brimming with fresh grapes and pears; and we opened our bottle of champagne.

Everywhere we went on the ship, Chris was greeted by new friends, both children and adults. Italian and Portuguese stewards and waiters had adopted him . . . They missed their own children they had left behind (their tour of duty usually runs from six to eight months, with time off averaging three months). They had brought him snacks and competed to seat him in the dining room -- never passing without greeting him by name.

Each of us had fun in our own way and we had memories of experiences that brought us closer together. Our cruise with Christopher had proven to be a real bon voyage.