Q. This was the best summer we've ever had with our two little girls (3 and 5). It was hectic sometimes and often exhausting, but a lot of good things happened.

We had a week's visit from my inlaws at both the start of the summer and the end of it, which was a lot of fun, and in July we had three weeks at the beach. For the first two weeks it was just our family -- a time to feel close and relax -- and then my parents shared the cottage for the last week, which was lovely. The children got a lot of outings and castle-building and I didn't have to cook one dinner!

But the best of all was getting the generations together. All the grandparents and my husband and I had the same reaction: We want to stay in touch much better than we have, for the sake of our children as well as for ourselves.

There are the occasional Saturday phone calls and some holiday visits, but our children aren't going to know their grandparents well unless we do something about it. My folks live on Long Island, my in-laws in North Carolina, and with my September-to-June teaching job I can't get away during the school year. How do other families handle this?

A. Probably the best gift a parent can give a child is a sense of belonging, and nothing gives this better than an extended family. Love comes in a lot of flavors and the richest children are the ones who know many.

To reinforce the visits, show your slides, movies (or videotapes), and show them every month or two. This may seem rather often, but the children may be the only truly appreciative audience these pictures will ever have. They will enjoy seeing their grandparents, and they'll love to see themselves. t

Show off the snapshots too. They don't give any pleasure sitting around in envelopes. Frame some, put some on a bulletin board in your children's room and others in photo albums, so you can flip through them together to talk over the good times, as if you were taking turns reading from a story book.

Then go back and dig up the pictures from your own childhoods. Your girls will like to hear about the olden days, although at 3 and 5 they are too young to understand that parents could ever be children, or that grandparents could be anything but grandparents. No matter. The idea amuses them just the same.

You'll want to encourage postcards, which are exciting both to send and receive, if they have pictures on them. Address a set for each pair of grandparents and let each girl choose from each set now and then. They can draw pictures on them, print their names as best they can, and stamp and mail them.

If you do this on special occasions, they will think of it as a treat and not a duty, even when it is supposed to be a thank-you note. The cards they get back make the custom all the better.

Your children also can send presents to the grandparents, the sort they pick up at a yard sale and you mail, unwrapped, in a manilla envelope. A dishtowel, a string of beads, a paperback mystery are all delights to buy. Every time people invest their time or their energy in someone else -- not because they must, but because they want to -- they treasure that person more, and this is just as true for children as it is for anyone else.

Phone calls are lovely, but tapes can be played again and again, which is why we think every family can make good use of a tape recorder. The grandparents can play and play again the brief snatches of conversation and giggles the children send, and, of course, they can send tapes too.

We know one thoughtful lady who sends her grandchildren new storybooks and tapes to go with them, so they can listen to the recording while they turn the pages. Bulletins of all sorts -- school, church, alumnae -- keep families in touch.

We think that it's very important that the young are in touch with the old. And although grandparents have a special role, there is no reason to limit the children's links. In fact, studies show that the worst segregation a child can know is not racial or economic, but the segregation of age.

That's why parents should make sure that their children know many older people, by visiting elderly neighbors, talking to the old couple at the grocery store, by running errands for someone in the neighborhood who is disabled.

We even think our older generation has a responsibility to keep in touch with the young. It's a two-way street, and fortunately it gets easier all the time.

The University of D.C. has a successful program called Close the Generation Gap, where older volunteers work with children in District elementary public schools.

Both men and women -- if they're over 55 and healthy -- can choose the school and the job they want, and after a brief training program work as tutors, arts and crafts teachers, lunchroom and playgroup monitors, club supervisors and nurse's aides. They usually work on four-hour shifts from one to five days a week, in exchange for lunch and transit fare from the UDC's Institute of Gerontology (282-7700) and a large measure of self-satisfaction.

It's a little far for North Carolina and Long Island grandparents, but the District should have enough of its own to keep your children busy.