It's a time for anniversaries. The U.S. Constitution has noted its bicentennial, and Tinkertoys is celebrating 75 years of imaginative and creative building.

Not many children's books have been in print 200 or even 75 years, but there are some that are celebrating a period of 15, 25, 30 and even 50 years. That's a long time for a book title to survive.Following are some celebrated books, a magazine and a publishing house that are worth noting:

This is the 25 anniversary of "Where the Wild Things Are" a picture storybook by Maurice Sendak. (Harper, 1963.) This book was chosen as the 1964 Caldecott Medal Winner as the Most Distinguished Picture Book of that year. Since 1963 it has sold more than 2 million copies and has been translated into 22 different languages.

Probably the best known of the 75 books Sendak has written or illustrated, "Where the Wild Things Are" met the artist's need to delve into the fear and terrors of children growing up. In it he allows a bored child, Max, to be propelled out of his room through days and weeks into a private place where he is in control. Sendak has fulfilled what his art has always intended to do: ". . . affect people on a passionate level. . . ."

People are passionate about Maurice Sendak and Max. They are accepted or rejected, praised or censored. Despite the controversy, they represent what readers want, an arena for the young as they relate to the fears of growing up or losing freedom and not being attached to a safe "foundation."

To many adults there is pleasure in the fact that an artist can capture the latent fears that often still haunt the waking hours and burden a troubled sleep.

Also commemorating a 25th anniversary is Avon Books, a leading publisher of paperbacks. Besides its own celebration, Avon will simultaneously be honoring birthday of "Amelia Bedelia." For 25 years, Amelia has been doing everything right but getting everything wrong. If she was asked to dust the furniture, she did it, literally. Weed the garden? Row upon row of weeds are transplanted in a grand manner.

The humor and simple text of the five-part series make Amelia Bedelia some of the most popular fare for early readers.

Amelia and Max will never grow up and that's just fine for most children.

Growing up and improving is what "Cricket" magazine has done during its 15 years in print. "Cricket," known as the `literary magazine' for children, features renowned and promising new authors, illustrators and poets working with a prize-winning editorial board. The magazine includes fiction, non-fiction, puzzles and recipes.

Highly illustrated - but in good taste - "Cricket" directs a message to young readers of ages 5 through 13 that excerpts of literature and short pieces are legitimate and encourages them to write in and express their reactions through the "Letterbox" section.

Author Norman Bridwell speaks about "Clifford, the Big Red Dog" as if the animal were lapping up puppy biscuits from a giant dog dish: "Although my books are geared towards a first- to second-grade reading level, I've found that older kids are as receptive to Clifford as the little ones. . . . I believe Clifford appeals to a universal dilemma despite his good intentions. . . ."

To Bridwell, and many readers, Clifford exemplifies the pleasure of being able to do many imaginary things; take care of a bully, stop traffic for important reasons and win friends everywhere. Clifford, although gangly and big (I mean HUGE!) is a gentle pet that will continue to be a delight to young readers for years to come.

Although the "Chronicles of Narnia" by C.S. Lewis (Atheneum) were completed over 33 years ago, the "picture" of this seven-volume fantasy series began in Lewis' head 25 years earlier. "The lion began with a picture of a faun carrying an umbrella and parcels in a snowy wood. The picture had been in my mind since I was about 16. Then one day when I was about 40, I said to myself, `Let's try to make a story about it.' "

Now, over 22 million copies later, the Narnia books provide young readers with suspense and adventure as they did in the past. Their message is unwavering, the protagonists are timeless. The books tell the experiences of British children who climb through a compelling wardrobe into an enchanted land where it is always winter (but never Christmas). In this land of Narnia, the children meet the great golden lion leader, Aslan, and help him free his subjects from the evil White Witch.

Full of allegory, illusion and philosophy, "The Chronicles of Narnia" are a mainstay of fantasy, a child's opportunity to read, react and re-read while always finding something new.

This year marks the 50 anniversary of Mr. Popper, the small-town housepainter, whose fantasy was to explore the Antarctic regions. Along with this memorable hero are Captain Cook and 12 other formidable penguins who take over the household, literally and figuratively, in "Mr. Popper's Penguins" (Little, Brown, 1938).

Now in fresh new cover and over-sized format, this amusing story with the distinctive side-line drawings of Robert Lawson becomes a book for family pleasure, classroom read-aloud and individual giggling.

For the celebration of the 50th year of "The Hobbit" (J.R.R. Tolkien, Houghton, Mifflin) a golden anniversary edition is being issued. This handsome slip-cased volume contains a foreward written by the author's son, Christopher, for whom the story was written. Tolkien's personal black-and-white sketches and maps are included, as well as additional color illustrations.

"The Hobbit," although listed as a fantasy for children and young adults, has captured readers of all ages. The tale of principled elf-like creatures and their adversaries in a detailed imaginary land became the basis of a three-volume series, "Lord of the Rings." Also written about ". . . in a hole in the round, there lived a hobbit . . ." are numerous compendiums that chronicle the language patterns of what many consider to be the treasured classical fantasy piece of all time.

So, it's celebration time for some literature that has retained its youth and vigor. As Max would say, "Let the Wild Rumpus start. . . ."