GEE," SAID JENNIFER, already into her eighth autumn and nobody's innocent. "Gee."

Jennifer was standing on the fringe around the Count's Ball Room at Sesame Place in Longhorne, Pa., watching 10 kids scrabbling their way to the top of a plastic pinnacle to dive into a two-foot-deep dry pool filled with what looked like all the blue plastic balls in the world. Below her a small boy almost submerged in plastic balls, only his head and a foot showing, was screaming to his mother to "look, look, look at me!"

I had not brought any smallfry with me, and I needed to observe some authentic reactions at close hand.

The reason there were only 10 kids in the Ball Room is that's all they let in at a time. It's the hit of Sesame Place and the brainchild of Eric McMillan, playground designer, who wondered idly what it would be like to crawl into a jar of pickled onions. It's a real drawing card, but there are plenty of others in the highly innovative, kid-powered, dayglow-colored new playground park that resulted from a collaboration between Busch Gardens and the Children's Television Workshop. Sesame Street's beloved Big Bird, Ernie and the rest lend the general design motif and it's absolutely true that the children enjoy the whole thing almost as much as their parents.

Sesame Place is street theater where everybody stars, from the little girl emerging triumphantly from a barrel tunnel to the happy father of three inching his way along overhead in the cargo nets strung above the crowd. The energy all this participation generates could light up a small shopping mall. From the moment you enter the gates you get a different feel than in theme parks where visitors are passive riders. Sesame Place just uncorks the bottle of imagination and stands back to let it all happen.

And the playground is only part of the fun. Inside, from the Computer Gallery, beckon an array of some 70 computer games, all of which are friendly and encouraging and sometimes even call the people who play them by name. Sesame Place has done the impossible and humanized computers.

What with all this, it's hard to choose. Outside, a child could lose himself forever playing hide and seek in the Monster Maze, a forest of brightly colored six-foot-high lightweight punching bags. And then there's Grover's Rubber Band Bounce, a giant rubber band four feet wide and eight feet high which turns everybody into a bouncing baby. And the Rubber Duckie pond, a giant water bed for walking on. And the Super Grover's Cable Glide where you can ride just a few safe feet off the ground clear across a section of the park.

Jennifer shook her head when she saw the Water Maze where the waiting line looked like the one for "The Empire Strikes Back." She preferred to slide down the pole into the dry labyrinth across the way. Scrambling through tunnels that emerge periodically into open-mesh chambers above water jets, the crawlers in the Water Maze get pretty wet. The spotlessly clean ladies' room of Sesame Place is full of pleased, soaked kids being blotted dry by parents after a go at this attraction. You wade right into the fun at Seasme Place, get wet, get happy.

The park is geared for children from 3 to 13, but everybody can enjoy things at his or her own speed. A wooden cutout of Big Bird holds a sign near the entrance telling visitors over 13 years old, or more than 5 feet 2 inches tall, they can play only on some attractions. I saw some reluctant oversize children being urged to join in by their parents, but that is not the park's fault.

Somewhere in the kaleidoscope of children I lost Jennifer, so, moving on to the Computer Gallery, I scraped acquaintance with Michael, 10, busy at a word game computer. He was pressing buttons that made letters walk onto the screen on little feet. The letters at first behaved like small boys at a birthday party, shifting themselves around and leap-frogging over each other, but as we watched they arranged themselves into shifting lines that suggested words. The quicker you guess, the higher the score, and Michael was good at it. When we had the word, Michael typed it out on the keyboard and the machine congratulated us.

Sesame Place computers are very personal. They say nice things to the people who play them. We kibitzed over the shoulder of a small girl playing a game that required her to push the red button when she first spotted the shooting star in a galaxy of twinkling asteroids. Her reaction time was recorded by the computer and relayed with encouraging words. "Far out," said the computer. "Your score is 380." When she tried again before we left, the computer was again congratulating her. "You are truly star quality," it was spelling out.

This feedback is deliberate. The experts who designed the computer gallery think computers will loom large in the lives of the kids playing them, eventually becoming as commonplace as the telephone and television were to their parents, and they want to make the children feel good about the machines. Everything has been done to turn an inanimate device into a friend. mBig Bird, Oscar the Grouch and the rest often host the computer games, and sometimes are their raison d'etre . One of the most popular games is a challenge to draw electronically a composite Muppet.

The parents can't keep away from the computer games. You see them everywhere, playing at drawing a pattern with children in their laps. And it's no wonder. Such marvelous things these computers can do with just a little instruction: help plan a lemonade stand, write a tune, play paddle tennis with or without gravity, freeze your shadow, paint a picture of your voice. And although you must pay a dollar for three tokens allowing you to play, you get four minutes of play time compared to the 90 seconds in most arcade games. No charge for scientific demonstrations, of which there are many.

The management at Sesame Place considers their new venture, pilot park of many that are projected, as more of a neighborhood park than a relation to large-scale theme parks, and they have kept the price smaller as well. General admission is $3.95 plus tax, a far cry from the cost at larger parks, and all the playground attractions are covered by this fee.

When you get hungry, even the Food Factory at Sesame Place is an experience.

All food at the Food Factory is prepared within full view. In the Greens Machine you can see them peeling, chopping and mixing raw vegetables and fruits. In the Dough Workshop, you watch them rolling flour into dough and putting it into the oven in the Bakeworks. You make your selection in a multiple short-order line and eat in a room the designers say is suggestive of the inside of a salad bowl. I never saw a salad bowl roofed with upside down umbrellas and lit by the bare bulbs used in backstage mirrors, but it comes off nicely.

The choices are limited as yet, but all are nutritious and include no fried foods, no greasy sacks of French fries. There are no preservatives, no empty calories, no food dyes, less sugar and salt. My wrap-around hot dog sheathed in a whole-wheat-flour wrapping was low in nitrite and cost $1.50. Michael, lent briefly to me so I could treat him to a bite, consumed a square-meal pizza with the same whole-wheat pastry for $1.75. We munched close to a huge cutout of Big Bird instructing us to wash our wings before eating and taste before salting. "Personally," said Big Bird, "I prefer my bird seed straight."

I wanted a piece of chocolate cake but Michael shook his head at me, roles reversed. "You can have an ice-cream cone," he said kindly. "They don't serve cake."

Even the ice cream is low in fat.

After Michael and I parted, I buttonholed two small girls headed for the ice-cream cones, arms linked, heads together.

What do you think of Sesame Place?" I asked the tallest.

They exchanged a glance that spoke volumes of the thickheadedness of adults.

"Very nice," said the older girl primly, grabbing her friend's elbow and bearing her off.

Sesame Place is open from 10 a.m. to 6 p.m. until Nov. 9. During the winter months, only indoor activities will be open, with hours 10 a.m. to 10 p.m.