A dozen three- and four-year-olds accompanied by one parent each marched in place in a back room of the Smithsonians arts and industry building. More or less in unison, they sang a variation of "The Farmer in the Dell," with gestures:

The Grand Old Duke of York

He had 10,000 men

He marched them up the hill one day (stand on tiptoes)

And marched them down again (squat).

And when you're up you're up (tiptoes)

And when you're down you're down (squat)

But when you're only halfway up (bend at the waist)

You're neither up (tiptoes)

Nor down(squat).

That was a typical beginning for "Let's Work Together," an arts-and-crafts program offered by the Smithsonian for six consecutive Sundays in the late fall. The class, which cost $32 including all materials, provided a number of activities and experiences capable of easily, if somewhat messily, being repeated at home. In fact, it made me wonder why such activities aren't carried out at home more often.

Like painting with shaving cream, an instant turn-on for any little kid who has ever thought about sneaking up on dad's shaving cream and letting fly. This gives kids a chance to do just that, only creatively.

First, Ross, my four-year-old son, spurted shaving cream on his hand and smacked my palm in a "gimme five." Shaving cream oozed down our wrists. Then he said, "Pretend like you don't know I have shaving cream and we shake hands." So we did. Soon shaving cream was everywhere, some even making it onto the large sheets of construction paper we were to "paint" on.

We swirled the cream around on the paper, and Ross ran his fingers through it, allegedly to make "roads" for the city he said we were painting. Then we sprinkled generous amounts of various colors of powdered paint, which partially dissolves in the shaving cream, leaving a misty, grainly look when the cream dried.

After a few more handshakes and "smooshing" of shaving cream, Ross dropped the city idea and dubbed our creation "Star Wars." A little water cleared us of our deed and we were left with a unique piece of art.

Arts and crafts activities such as shaving-cream art and others can open new doors in the parent-child relationship. In my case, the activities probably gave Ross a more surprising glimpse of me than vice versa. Dad slapping shaving cream around indiscriminately instead of neatly applying it to his face? Dad with scissors, glue and paint? Dad singing? "Grand Old Duke of York"?

Why not? To get involved as an adult in a child's art-and-crafts experience provides a good reason to revert to childhood and its childish instincts. Kids pick this up and they seem to say, "If it's okay for dad, it's okay for me." Then their imagination and enthusiasm take over. Creativity is the result.

Ross is a happy-go-lucky child, and his arts and crafts activities - in both the process and the final result - reflect that. It doesn't take an analyst to see it: He draws big circles, adds to his work spontaneously, delights in mixing odd colors.

Kids derive obvious satisfaction from saying, "Okay, now let's dump some of that paint over here," running their fingers through it and deciding that it's a rainbow. And then, minutes later, saying the same thing is a highway.

Call it artistic freedom or call it a mess (only not loud enough for your child to hear). Resign yourself that there will be some cleaning up to do, spread out some old newspapers, warm up with the "Grand Old Duke of York," and try some of the following with your child: MOBILE MAKING

Have your child draw four (any number will do, but four makes it easier to balance) things he likes on different-color sheets of construction paper. Cut the drawings out and punch a hole in the top of each to thread a string through. Tie the drawings to two sticks that are crossed and tied together. Tie another string to the point where the sticks cross and hang the mobile from a ceiling hooks so it dangles freely. CITY OF BOXES

To make this activity easier for a child to visualize, try to show him a picture of a cityscape before beginning.

Paint a heavy piece of cardboard and several cereal, cake-mix and other boxes varying in size. Glue the boxes to the cardboard, varying their placement - putting some sideways, other lengthwise and some at angles - until, perhaps after some careful looking, a multicolored cityscape is formed. SAND PRINTING

Have your child draw a design with paste (preferably the standard white kind that someone always try to eat) on a piece of construction paper. Once the design is drawn, shake powdered paint that has been mixed with sand over the pasted areas. The sand provides a grainy texture and some it, along with the paint, will stick to the paste.

Now comes the time for decisions in sand painting. You can stand the construction paper on edge and gently pat it so sand and paint drift down the paper, providing a [WORD ILLEGIBLE] effect. Or take a thin paint brush [WORD ILLEGIBLE] smooth out some of the grainier areas for contrasts. Or do a combination of both which causes a surrealistic effect - globes paint and sand on a misty background. Or just leave it alone.