Ever watch an eight-year-old's face light up when a chunky trout is swung from the water and lies flopping on the grassy bank? Kids and fishing go together like chimps and bananas but these days it's hard to find a place where youngsters can enjoy themselves. There are plenty of spots where bluegills and such can be caught, but there is something special about stream fishing for trout and every child should have a chance.

One problem is that after the spring stocking of trout hordes of adults swarm to streamside and within a matter of weeks have fished them out. Then there are the parents who have never done any fishing and suddenly discover that a son or daughter wants to. The parents, who may excel at tennis, golf or making money, don't know the first thing about tackle or trout.

Pennsylvania is one state that recognizes the problems of young fishermen and has set aside sections of streams for children only. One of the nearest is a quarter-mile stretch of Yellow Breeches Creek in Cumberland County, about two hours from Washington.

The Breeches ranks with the best trout waters in the country. Just downstream from the children's section is a specially regulated fish-for-fun area where top fly fishermen usually can be found testing their skills against the wily brown trout. But kids usually aren't interested in all the fancy refinements, they just like to catch trout. It makes no difference if the fish take a worm or a Royal Coachman dry fly.

Common garden worms are still a popular bait but Velveeta cheese and canned corn are also very effective on today's trout, and they're a lot simpler -- or cheaper -- to get.

The children's section of the Yellow Breeches is several feet deep and rather slow-moving, making it good water for fishing with bait. The bank along one side is cleared and grassy, with a walkway set back from the edge for easy access. Fishing tactics are simple: The bait is cast out and allowed to settle to the bottom. Then it becomes a matter of waiting for a bite.

Keep tackle simple; a closed-face spinning rig is best. The Daiwa and Zebco mini-cast outfits are an excellent choice; the reels are permanently mounted on the rods and can be had for as little as $10. Most such rigs come with line already on the reel. It may be best to replace it with premium monofilament, since some factory-spooled reels come with stiff monofilament that's hard to cast and easy to tangle. Something around six- or eight-pound test should be adequate.

Take along plenty of hooks and sinkers, because snagging on the steam bottom is a common problem. Buy hooks in size 4 or 6 and a box of split shot for casting weight.

Resist the temptation to fish for the child, who may be quite clumsy at first. Give plenty of advice and moral support but let them do the fishing. Once shown how, a child who really wants to fish will bait his or her own hook. HOW TO DO IT

In addition to the Yellow Breeches there are many other sections of streams set aside for youngsters. For information contact the Pennsylvania Fish Commission, 3532 Walnut Street, Harrisburg, Pennsylvania 17120. Such waters are restricted to children 12 years of age or younger and no license is required, even for nonresidents. For exact directions to the children's section of the Yellow Breeches, stop in to see Bill Skilton at the Yellow Breeches Fly Shop in Boiling Springs or call him at 717/258-6752. AN ALTERNATIVE

If Pennsylvania is just too far, take the kids to the Fountain Rock Springs trout farm just outside Frederick, Maryland, where it's fish-for-pay but fun anyway. Admission is $1 for adults, 50 cents for those under 12, spectators free. Rods rent for $2.50 a day, and the charge is $2.75 per pound of fish (every trout caught must be kept). To get there: I-270 to U.S. 15 north at Frederick; four miles on to the Biggs Ford Road exit and another mile to Fountain Rock Road; take a right and look for the sign.