The crunching of celery. The bouncing of dice on a wooden table. Quiet laughter and frantic calls: "Tyler, com back -- we need those dice."

To Laurie Greenberg and Jamie Harms of the Smithsonian's Chesapeake Bay Center for Environmental Studies, these are the sounds of families learning about sciene together.

"Each family has itw own style of learning," said Harms. "That's what makes it exciting."

To find out how families learn, Harms and Greenberg send free Smithsonian Family Learning Project packets to interested families once a month -- along with a questionnaire about the project. One recent afternoon, the two young scientists demonstrated the projects to families -- most of them tourists -- at the Museum of Natural History.

The Chastains of Utica, Michigan -- none of them overweight --were playing a board game called "Survival of the Fattest" and learning how people gain and lose weight. Their next vacation, they were told, will be a trip to Mars. Since their spaceships won't be able to carry enough food for the 20-month round trip, they are advised to gain weight -- 150 pounds each.

"That wouldn't even be fund -- but 20 would be," said Sue Chastain, mother of Christie, 14; Steven, 12; and Denise, seven. The players have a year to gain the weight, and each space they advance around the board by a roll of the dice represents one pound. There are also cards to draw -- which can mean losing weight and sliding backward on the board.

"Your braces are too tight -- eat soup for two days," instructed a card drawn by Christie, who doesn't wear braces ("thank goodness").

Her younger brother, however, gained a few pounds by downing 12 pies in a pie-eating contest.

"Could you really eat that many?" asked his mother.

"If they were cherry or blueberry I could," affirmed Steven.

But it's Denise, who weighs about 50 pounds in real life, who gained 150 game pounds first -- after the Easter Bunny delivered a bumper crop of chocolate eggs.

The weight-gain strategy isn't really reasible or appropriate, the family was told, but the point of the activity was to get them to thinking about the functions of fat.

While the Chastains were thinking about fat and food, at another table the Floreks of Piscataway, New Jersey, were dealing with food in the flesh, in an experiment called kitchen botany. They were issued a plastic bag containing an apple, a carrot, some broccol, celery, a cucumber, a peach, a potato, a tomato and a green pepper and told to put all the fruit on one side of the table and all the vegetables on the other. This is harder than it sounds, and even after they were told that if it has seeds it's a fruit, there was some question about the broccoli.

"Are these seeds?" asked nine-year-old Christopher, pointing to the florets.

Greenberg explained that when we eat broccoli we are really eating the flower buds, and that it you let broccoli grow too long the green buds turn into a bouquet of yellow flowers, a phenomenon that Christopher remembered seeing "over at Grandpa's."

After learning that they could also eat the roots, leaves, stems and stalks of many plants and that tomatoes are berries but blackberries and raspberries really aren't -- they're drupelets, botanically speaking -- the Floreks were getting hungry. Greenberg produced several kinds of dip, and the stems, stalks and roots were cooled and eaten.

"Do they give you anything to drink?" whispered Donna, seven, chomping on a green pepper.

After signing up the Floreks and the Chastains for the SFLP-of-the-month club, Harms and Greenberg explained the project.

"It's still in the development process," said Harms. "We want to find the best and most appropriate projects for families. Then we'll refine them and look for a publisher. We've been going for two years now, and we've developed 60 activities."

"Families are an important learning group," added Greenberg, "and it's wonderful to watch them together. One of the most exciting moments for me came when we were doing a lawn paper project -- making paper out of grass cuttings. There were these kids - who were probably not allowed to touch the blender at home -- grinding up grass in a blender. And there was the father, who probably never touched the iron at home, teaching his son how to iron the paper."