SESAME PLACE makes you glad you have a kid. And if you don't have one, it'll make you want to rent one -- or be one -- for a day.

More exciting than a playground, less regimented than a theme park, this family fun place bills itself as a 21st-century action-oriented play park. What sets it apart -- and above -- other amusement parks is that it's designed with young kids in mind. It's vertical, and mostly outdoors, with activities and equipment stacked cleverly in a compact four-acre space.

Just half an hour north of Philadelphia, Sesame Place is an explosion of primary colors after the monochrome gray of I-95. Yellow, green, red and blue towers reach for the sky. Multicolored pennants wave from the Lego-like battlements. The whole complex looks like a big, wacky plastic-brick toy.

"Sesame Street" characters and allusions abound -- all the garbage cans have "Property of Oscar the Grouch" stamped on them -- making for instant recognition among the younger set.

The folks at Sesame Place are, in fact, the same creative educators who've been beaming "Sesame Street" into your living room for the past 18 years. The Children's Television Workshop designed this "play-as-you-grow park," aimed at kids three to 13, with Busch Entertainment Corp. (of Busch Gardens and other amusements fame). But there's nary a motorized ride nor a can of beer on the premises. There is, however, plenty of fun and excitement among the 40 or so imaginative play activities plus the water rides, computer games, science experiments, shows and working television studio.

The action starts the moment you push past the turnstile and climb a flight of stairs straight into the wide-open beak of a gigantic Big Bird cutout. From there you jiggle across a slat bridge to Oscar's Observation Tower, where you can take in the whole park before sliding down a slippery tube into a play area so enticing the kids won't know where to run first. It's a little like Alice's tumble into Wonderland.

At ground level, you can fight your way through a Monster Maze of lightweight punching bags. Or you can take off your shoes and venture out onto Ernie's Bed Bounce, a brilliant-blue oversize air mattress on which you're supposed to jump. But there's absolutely no resistance, so it's hard to get off the ground. It's hilarious -- and a real workout -- to try, though. (I know because I did; grownups are welcome to jump right on with their offspring.)

Before you lace your shoes back up you can flounder around in The Count's Ballroom of 80,000 -- count them! -- plastic balls on a squishy trampoline surface. After years of watching kids sink into similar plastic seas at pizza parlors and carnivals, parents can dive in here and find out what it feels like -- cold, clammy and very weird.

Just above ground, there's Mumford's Water Maze, a labyrinth of opaque plastic chambers and tubes that spray water as you crawl through. And there's Cookie Mountain, a slippery blue vinyl mountain that under-7s can attempt to climb.

Meanwhile, high overhead -- as high as three stories, in fact -- are swinging cargo nets crawling with kids and grownups scrambling across wide expanses of netting connected by swinging tunnels and net tubes.

But before Emily, 7, and Sorin, 8, could do justice to all three levels, laughter spilling out of a canvas tent drew them into the Circle Theater, where one of the Sesame Players was warming up the audience with groaningly bad knock-knock jokes -- "Knock, knock/ Who's there?/ Dwayne/ Dwayne who?/ Dwayne the bathtub, I'm dwowning!"

Using minimal props and maximum audience participation, two energetic young actors took the audience through a 20-minute story in which kids from the audience played the major roles and the whole audience chimed in with choral responses.

After this first whirlwind hour, we changed into bathing suits and headed for the colorful and inviting water area. After some splashing around in the Count's Fount, a shallow pool with nets, slides and water toys that kids activate, the girls got their courage up to try the Slippery Slope, a six-lane water slide that bumps you along 75 feet and down 15 feet into a pool of water (you have to be over four feet tall). For half an hour Emily and Sorin slipslided happily away. Then they geared up for the big one -- the Sesame Streak, a three-story water slide.

For this, you grab a two-person rubber raft (kids under 48 inches have to ride with an adult) or a solo inner tube, then climb to the top of a tower, seat yourself (awkwardly)in your raft and off you go -- careening down one of two twisting chutes. The flumes make great echo chambers for screams and whoops, of which there are plenty. It's thrilling and chilling, especially when you splash into the pool at the bottom. But mostly it's sheer delight.

This is one ride that'll keep the most hyperactive kid happy and bring out the kid in any grownup, like the 40ish guy who was beaming like a four-year-old as he stood dripping wet with an inner tube tucked under his arm. Who needs Club Med?

If you tire of streaking, there's also the Big Slipper, an even taller body water slide, and Runaway Rapids (closed the day we visited) that's billed as a "wet and wild whitewater raft ride down a 350-foot turning, churning course." There's a tamer version for younger children called Rubber Duckie Rapids.

Waterlogged and worn out after 1 1/2 hours of water games, we headed for The Food Factory. It's an inside-out complex with all the workings exposed. Green tubes snake along the blue ceiling, red pipes mark the waiting lines and glass houses enclose young workers busily assembling food that's fun and good for you. The menu lists the nutritional value of every item. The wholewheat pizza, for instance, is supposed to provide 50 percent of an adult's daily protein and Vitamin A requirements and the 1/4-pound all-beef hot dog is guaranteed to be low in sugar, salt and fat. Fiber-conscious moms can buy a bag of crispy vegetables (rich in vitamin A and C) for kids to munch on. The milk is 2 percent and the cookies are made with carob chips.

At our table -- you can eat inside or al fresco -- the pizza was a big hit as were the Curly-Q Bake Fries, non-greasy, richly potatoey spirals that doubled as food and amusement. Little girls quickly discover they make great corkscrew curls or dangling earrings. The food wasn't cheap -- we spent about $18 for a very hungry four -- but it tasted great.

After lunch, with the sun at its height, we cooled off in the Computer Gallery, a dim cavern filled with 50 or so colorful computer terminals loaded with educational games aimed at under-7s, 7 & up and over 9 years old. This is the only activity you pay extra for at Sesame Place; tokens are 3 for a dollar and if your kid is a real computer whiz, she might be able to run through $5 in an hour.

After six games each, the girls spent 15 minutes posing in the gallery's Rainbow Room, a dark room with a huge screen on which your image, passed through a special-effects generator, is projected as a rainbow of colors. And there's a hands-on lesson in centrifugal force and gravity at the Gravity-Go-Round.

Back in the sunlight, we ran into a life-size Bert, who was getting a big hug from one toddler while the surrounding grownups oohed and aahed. A towering shaggy blue Cookie Monster, on the other hand, elicited screams of delight from some kids and prompted others to run for cover behind a parent's legs.

Over at the Sesame Studio, we promptly lost the girls among the 20 science activities spread over two roomy floors. Here, you can make your own movie by drawing characters on a strip of paper and spinning it in a drum called a zoetrope, listen to music made with your footsteps, see yourself "float above the ground" through symmetrical reflections, manipulate laser beams, see how much electrical energy you can generate by pedaling a bike or create a shadow picture on a liquid crystal wall surface. Plus you can actually walk on Sesame Street, a working replica of the television set.

If you're there at the right time for Sesame Dream Network, you can also costar with Big Bird and Oscar in a prerecorded video show. We missed the show but watched ourselves on the closed-circuit TV monitors and snapped pictures of the girls sitting on the famous brownstone steps and standing behind a life-size Ernie taking a bubble bath with his rubber duckie.

Saving the Studio for last was a mistake. The girls emphatically did not want to leave. But, then, no matter where you begin or end, there's so much to do at Sesame Place, you're probably always going to go away wanting more. SESAME PLACE SEASON

Sesame Place is open 10 to 8 daily through July 5, 9 to 8:30 through August 30 and 10 to 5 on weekends through October 11. Through Labor Day, admission is $13.15 for kids 15 and under and $10.95 adults; children under 2 are free. A family of mom, dad and two school-age kids should count on spending about $70, including food, a locker and computer games. Season's passes are also available. 215/757-1100. MAKING THE MOST OF THE PARK The park, which can hold up to 6,000 visitors, has special activity areas for preschoolers and a few of the activities have height or age guidelines. There are lots of shaded areas with tables and chairs -- even an official Parent's Oasis -- for grownups to relax yet keep an eye on the kids. Restrooms are plentiful and well-kept. There are change rooms in the water area and lockers can be rented from a desk in the Computer Gallery for $3.

Services include a nursing area, a diaper-changing area, a Lost Parents office and a well-staffed, bright first-aid clinic. (We found this last out by way of Emily falling down on the pebbly concrete surface around the water area.) Kids should wear shoes, or at least plastic or rubber sandals.

Beyond the Food Factory, there's a Sandwich Shoppe, plus fruit juice bars throughout the park. The Food Factory staff was friendly and agreeable about warming a baby bottle in the microwave. We also spotted do-it-yourself families arriving with large coolers to take advantage of the park's two picnic areas. HOW TO GET TO SESAME PLACE Sesame Place is in Langhorne, Pennsylvania. Take I-95 north past Philadelphia to the U.S. 1 North/Morrisville exit; continue on U.S. 1 to the Oxford Valley exit and watch for Sesame Place sign right beside the Oxford Valley Mall. Amtrak also offers a Sesame Place Express from D.C. for about $65 adult, $42 for 12 and under. Call 800/USA-RAIL.