Taking care of preschoolers requires humor, imagination, and patience

If you've chosen to concentrate on child care at home during those important preschool years, you're sure to find yourself making friends with parents of other toddlers and tots.

Maybe you exchange babysitting time with these friends. You try to provide a happy, relaxed atmosphere, and the little ones seem to have fun at your house. Then you're suddenly asked to care for one or more children as a paying proposition. (Here we'll be talking about helping out friends and neighbors for the odd hour, half day, or week, not licensed day care.)

Your home is already babyproofed and equipped with toys, child-sized furniture, maybe a swing set or sandbox outside. The job would offer companionship for your own youngster(s) while providing welcome income. Meanwhile you're in for a lot of pleasure and a fascinating learning experience, which could have career value in the future.

A houseful of preschoolers requires a ready sense of humor and lots of imagination and patience. If this is your first baby, or if you aren't from a large family and haven't had the opportunity to work with young children, you may find this free-wheeling assignment more challenging than you'd expected. At least we did, with our first child.

What do you do, if yours is the place preschoolers love to come? Most valuable is firsthand observation or a friend with lots of experience.

Here are some dos and don'ts that can help make this a successful and rewarding experience:

* Safety first: Especially if the children's ages differ and you're beginning to ''trust'' your own son or daughter around the house, check over your surroundings again with the eagle eye of a curious two-year-old newcomer.

* Write down your house rules. Of course your list - covering play areas, toys, snacks, TV - will differ from anyone else's. The important thing is to make a decision about every debatable aspect of the play situation. Discuss your rules with parents of potential playmates; they should back you up, even if they handle things differently at home. Revise until you feel comfortable with your rules, then plan to be rather firm about enforcing them.

* When youngsters arrive, immediately clue them in on where to play, and with what. My skilled-parent friend always insisted that her children and friends entertain themselves in a specified play area - bedroom or family room - while parents conversed nearby. The playfellows were welcome to bring in their enthusiasm or problems, but were then urged to return to their toys. Although with toddlers this at first seemed too much to require, I was very impressed later with the way youngsters applied themselves to their play in her home - and continued to apply themselves! Part of this mother's success was surely the friendly but matter-of-fact tone in which she laid down her house rules.

* Store up in advance a few ideas for the children's amusement each time, with quiet pursuits preceding sociable play. I noticed that this was the sequence of each play session at the Infant Study Center our son attended (and it applies to older preschoolers, as well). Upon arrival at ''school,'' the five one- and two-year-olds became quickly absorbed - with their teacher's help and encouragement - in self-contained manipulation of fitting toys. The attention span of some lasted up to 30 minutes. Then they began to roam about companionably, pushing wooden trucks across the floor or playing house in the ''cooking corner,'' again for almost 30 mintues. After toileting and snacks, their morning was climaxed with free play,if possible out-of-doors riding tricycles, swinging, climbing. The alert teacher was always flexible. And she varied play location and activities as much as the situation allowed between one 90-minute meeting and the next.

* Don't confuse children with too many toy offerings. Ask if he/she wants to play with the blocks or the pounding board. And be sure your suggestions are appropriate to young visitors' ages and abilities. A one-year-old won't be able to join your almost-three, for instance, in simple puzzle work, but would enjoy playing with blocks alongside. Also, where feasible provide duplicates of favorite toys that always cause a contest. Or stash the item away for a while. It may be a year or two before these little people understand much about sharing and taking turns.

* Be present but unobtrusive. Unless needed, don't talk a lot. And don't flit about. The youngsters want to know that you're right there, quietly in charge. If you contentedly settle down to work nearby - gently rattling around the kitchen, tapping a typewriter, running a sewing machine - it's easier for them to settle down to their play.

* ''Never interrupt contented children,'' my skilled-parent friend advised. Be flexible with snacks and meals, waiting if you can until children seem to need them. If you distract them, might have trouble settling down again.

* Keep some surprises on hand for a rainy day. Let them fingerpaint at the kitchen table or sail boats in the bathtub, for a change. Make a list of their favorites for future reference.

* Try to end play sessions on an upbeat. When little ones show signs of weariness, let them help with toy pickup and get them ready to go home, or down for naps promptly.