The wonder and meaning of castles are brought to PBS

Childlike curiosity and wonder are qualities that too often tend to dissipate as we gain worldly experience and sophistication. Author-architect David Macaulay has not only retained his sense of curiosity and wonder within himself, he has also managed to transmit those characteristics to a whole series of fascinatingly readable books. Aimed generally toward juveniles and dealing mainly with architecture, these books, published by Houghton Mifflin, include the titles ''Castle,'' ''Cathedral,'' and ''Pyramid.'' And now, with Castle (PBS, Wednesday, 8-9 p.m., check local listings for repeats), that same curiosity and wonder have been successfully transferred to the television screen.

''Castle'' is the first in a series of unique programs based on Mr. Macaulay's books which one hopes we will be seeing during the next few years on PBS. It is a quaint - and triumphant - show, probably one of the most exciting programs for the whole family in all of television today.

Are the Macaulay books and the TV shows aimed at children? Yes. But they are aimed at adults as well - at anybody who has managed to hold on to a sense of excitement about the wonders of the world; anyone who can still vibrate with the excitement of expanded knowledge. The summing up, at the end of the TV show, is as straightforward as Macaulay could make it. There is no attempt to ''talk down to the kids.'' Macaulay obviously assumes that anyone watching the show - child or adult - is intelligent enough to understand a solid, well-thought-out conclusion.

''Castle,'' the TV show, combines clever animation with live episodes as Mr. Macaulay and actress Sarah Bullen discuss the roots of 13th-century castle architecture, wander about the sites of real Welsh castles, delve into the mysteries of everyday medieval life, and explain how towns evolved from isolated castles. In a way, it is a bit like ''Snow White Goes to College.''

While the drawings are not Macaulay's (his are much better), they are based upon his work. And he has supervised the production of the show, so viewers can count not only on authenticity and entertainment, but also on a special treat: intellectual stimulation. And TV viewers have an added bonus which book readers lack: the physical presence of David Macaulay himself. A chat with David Macaulay

I was treated to that same bonus the other day when Macaulay came calling to talk about the show. He brought along his eight-year-old daughter, a charming little girl who had obviously inherited her father's sense of wonderment: She listened intently as her father talked.

There's a little bit of the pixie in David Macaulay, a man who seems to revel in the adventure of scholarship. This former chairman of the illustration department of the Rhode Island School of Design has written nine ''construction'' books (including ''Castle'') and has won many awards.

Mr. Macaulay studied architecture at the Rhode Island School of Design ''and then in my fifth year realized that I didn't want to be an architect. So I left school, taught a year of art, and found some free-lance illustration work. But I soon got so tired of fitting a little frog next to the pond into the prescribed square next to a horrid little verse that I thought, 'If I can illustrate this stuff, I could write something better than this.' So I tried and that's how it all began.

''But architecture for me has always been the easiest way to study history. There is the proof; all you need is some clue as to how to translate it.''

Does our own society differ very much from the 13th-century society depicted in ''Castle''?

''Well, we're still concerned with survival. I suppose the people in the middle ages had certain advantages, and it might have been a bit easier for them to keep track of their priorities. For instance, if somebody shot an arrow at you, you simply stood behind a protective wall. Nowadays, arrows come from all sides.''

Macaulay believes that young people are able to absorb much heavier program content than most book publishers and TV programmers give them credit for. ''If the text gets a little dry, illustrations, if handled properly, can bridge over that.''

Does Macaulay believe there's a need for more books and TV shows that both adults and children can share?

''Absolutely. There should be less and less need for age categories. If there's something about a book or a television show which makes it universally enjoyable, there's no reason why both adults and 10-year-olds shouldn't enjoy it together.

''We've gotten into a trap with this age thing . . . especially in books. Some people try for 8-year-olds, others for 12-year-olds. But if you enjoy what you've done and you've done a pretty good job, then I think it is likely that you will reach a much broader audience than you might have anticipated. As long as you are not condescending.

''Too often there's a tendency to want to play down the information and concentrate more on entertainment - cover it with so much sugar that after a while it becomes nauseating to watch or to read. But I think if you are straightforward, whether it be for television or for books, if you use the visual stuff effectively, you can reach much broader audiences.''

Will commercial TV ever reach the point where it dares to do that - ignore the research demographics about age and allow writers simply to write good shows that will search out their own age levels?

''No. They're too frightened to try that. It's threatening because they've created their own barriers . . . a mind-set which does not permit them to break out.''

The next project for Macaulay is a TV version of his book ''Cathedral,'' for which he was preparing to go to France to shoot some film for the show. ''Among my books, there's also 'City,' about a Roman city, 'Pyramid,' and 'Underground.' They'll probably be TV shows. I've also done 'Great Moments in Architecture' and 'Motel of Mysteries' for Houghton Mifflin, just to have fun. I just finished 'Mill,' about the texile industry in a New England town of 1870.''

Why does the end of the ''Castle'' TV show, unlike the book, dispense with any attempt at easy whimsy and instead sound like David Macaulay talking to his own comtemporaries?

''There was a lot of entertainment stuff in 'Castle.' A lot of back-and-forth between Sarah and myself to make the whole entry into 'Castle' a playful thing to understand. But I wanted also to make the point that the castle was ultimately a weapon of war.

''It is important that viewers understand that, so they can better understand the people who lived in the castle and the people who tried to attack it. And maybe even understand just a bit better how and why so many cities in Europe have evolved from castles. And the historical background to many present-day fortress attitudes.''