Q: Here it is, three weeks before school starts, and I realize that I've hardly done anything with the children (a daughter, 10, and sons, 7 and 4) except swim, bike, drive them to day camps and Bible schools, take them on a few outings and sort of hang out with them on the porch. None of us has gotten much done.

I still would like to do some things that we all would enjoy and remember and possibly continue during the year. I'd like some activities outside and inside and maybe some books to get the older ones a little more excited about school. Any ideas?

A: There's nothing like the promise of September to bring out the guilt--and the resolutions--of parents in August.

Fortunately, this has been a good year for some books to inspire both you and the children, but some of the best books will be on your own kitchen shelf. There's nothing like cooking to teach your children pride and to give all of you a good time.

Other books are geared specifically to children. Your youngest will enjoy the activities in Fun Things To Do With Little Kids by Sally Claster Bell (of "Romper Room") and Dolly Langdon (Doubleday, $7.95) and those in the Johnson & Johnson book, Your Preschooler (Collier; $10.95), also full of advice.

A gardening book, Ladybugs & Lettuce Leaves (Center for Science in the Public Interest) is written for children to give them a chance to put ecology into practice. Together, you'll learn how to bottle black swallowtail caterpillars with some green leaves--and release them as butterflies in two weeks--and how to do in slugs (with dishes of beer) and aphids (with hot pepper spray) without harming the worms and ladybugs. It's a dandy book--although rather badly bound--and is available at CSPI, 1755 S St. NW, Washington, D.C. 20009, for $6.95, including postage. (The teacher's edition: $8.)

There are two neat books for your school-age kids. One is A Day in the Life of the World by Andrew Bailey, a small round book (Doubleday, $2.95), loaded with facts about the world today. The other is a book for tomorrow: The Kids' Whole Future Catalog by Paula Taylor (Random House, $6.95). It's full of talk about floating cities, sailing bicycles, people-powered planes, homemade robots and hundreds of other possibilities, with names and addresses of the books, posters and games that can be ordered to learn more.

Both of these books would be good introductions to The Science Book by Sara Stein (Workman, $6.95), one of a growing number of well-written books that intrigue children with their mild wit and fascinating scientific projects.

There is also an informative series of Science Club books--Super Motion; Liquid Magic; Light Fantastic and Amazing Air--(Lothrop, Lee & Shepherd), which are probably easier to find at the library than the bookstore. They are more old-fashioned (which means less witty) but perhaps more scientifically in-depth.

And if you think your daughter would like to pursue the traditional male areas, you can follow the advice in How to Encourage Girls in Math & Science by Joan Skolnick, Carol Langbort and Lucille Day (Spectrum; $7.95). It's designed to show parents and teachers how to help girls feel as comfortable in these subjects as boys.

But heaven forbid that the last blush of summer would get so leaden a child would forget that a vacation is made for fooling around--for swimming, and biking and hanging out on the porch. It's for quiet times alone; for brothers and sisters playing together; for family walks and talks. And it's for reading too, the best way to cram joy into these last weeks.

By all means check the latest by Roald Dahl. The BFG--as in Big Friendly Giant (Farrar, Straus & Giroux, $10.95) will delight your daughter and she'll giggle with glee to read his Revolting Rhymes (Knopf, $9.95) to her little brothers. In this book all the beloved fairy stories are parodied in verse, such as "Goldilocks": This famous wicked little tale Should never have been put on sale. It is a mystery to me Why loving parents cannot see That this is actually a book About a brazen little crook.Had I the chance I wouldn't fail To clap young Goldilocks in jail

And so it goes--one of a half-dozen long, jolly poems that will tickle the 4-year-old, make the 7-year-old feel quite daring and delight the 10-year-old who still likes to read her favorite fairy tales but is willing to poke fun at them, too.

She'll also like a Beverly Cleary book--who wouldn't?--but the best of all will be the classics you read to your children. Let them hear Shel Silverstein's poems and meet Winnie the Pooh, Madeline, Eloise, the Velveteen Rabbit, Harriet (the spy), Stuart Little, Charlotte--that wonderful spider--Peter Pan and the Little Prince.

If you feel you must justify this read-aloud time, remember: Children choose good literature when they have been able to contrast it with the rest.