If you're thinking of taking a cruise, and smallfry are tagging along, a good travel agent should be able to tell you which lines cater to families. Not all ships are "equipped to handle kids," notes American Express.

Does this vessel you've tentatively selected offer a playroom, supervised activities, special shore excursions? For what age groups and on which sailings? Will one stateroom be big enough for adults and children? What are the discounts for children, and what are the age limits? These are good questions to ask before you book passage.

Three Washington-area travel agencies are planning cruise shows for September-October.

Cruises Unlimited, 1825 K St. NW, has scheduled a "Cruise & Travel Show" at Le Champs, Watergate Mall, on Sept. 27 from 10 a.m. to 6 p.m. Representatives of cruise lines, airlines, and Club Mediterranee will be there to answer questions, and among the door prizes to be awarded are three cruises for three couples. Admission is free.

Old Town Travel, 404 King St., Alexandria, will sponsor their first annual "Travel & Cruise Show" on Oct. 4, from noon to 7 p.m. in the courtyard of the Old Town Holiday Inn, 480 King St. Representatives of cruise lines, airlines and Caribbean tourist boards will participate, and slide and film presentations will be shown about every half-hour. American Airlines will give a packing demonstration, and there will be music and door prizes. Admission at the door is $5, which includes a Frankie Welch fashion show. Net proceeds will benefit Alexandria Hospital.

Omega World Travel, Skyline Shopping Mall at Bailey's Crossroads, Va., will hold its second Washington Cruise and Travel Show on Oct. 12 from noon to 5 p.m. at the mall. All major airlines and cruise lines are expected to be represented, according to Dan Bohan, secretary-treasurer of the agency. The show will be presented in two Skyline theaters and the three major wings of the mall. There will be films, live entertainment and door prizes. All proceeds from the $2 admission charge will be donated to a local charity. The first show last March drew 2,000 visitors, Bohan said.

"Freighter travel is alive and well," maintains the Freighter Travel Club of America, P. O. Box 12693, Salem, Ore, 97309.Founded in 1958, the club charges a $12 annual fee which entitles members to receive "Freighter Travel News," a monthly publication featuring first-hand reports by freighter buffs on their worldwide trips.

Many travelers complain that they have difficulty finding agents who can provide information about freighters, and containerization and other factors have certainly affected itineraries and availability of vessels and passenger space. But the club said recently that "there are more cabins currently available aboard these "workhorses of the seas' than there has been for some time."

"Costs are up, as with everything else, but it's still the best travel buy anywhere," according to an official of Freighter World Cruises, 180 So. Lake Ave., Suite 335, Pasadena, Calif. 91101, a travel agency that books only freighters. Fares per person, double occupancy of stateroom, are now running between $45-$85 a day, she said.

The firm obtains visas for clients who come from "all over the country" and keeps them informed by phone, at no charge, about fluctuating departure dates. To enjoy freighter travel, you must be very flexible, since the needs of cargo always take precedence.There are no guarantees about countries visited or number of days in port. The agency receives a commission on sales from the freighter lines, thus there's no charges for its services.

Freighter World Cruises publishes a biweekly "Freighter Space Advisory." A year's subscription costs $13. But bear in mind that many vessels listed carry only 12 passengers, so it's necessary to move fast to secure a cabin (on some popular routes you still must book a freighter a year or more in advance).

Another way to go about finding a freighter is to buy a copy of "Ford's Freighter Travel Guide" (Ford's Travel Guides, P. O. Box 505, 22151 Clarendon St., Woodland Hills, Calif. 91365, paperback, $4.95 postpaid). It lists major lines, routes, typical fares, and other facts, but not current sailing schedules. When you find a line serving the area of the world that interests you, you must then contact the firm directly for information on sailings and space availabilty.