Story of true giving; Aunt Nina and Her Nephews and Nieces, by Franz Brandenberg and Aliki. New York: Greenwillow Books. 28pp. $10. Ages 3-8.

Anyone who is an aunt or has a favorite aunt will love this story about the riches that come from true giving. Single Aunt Nina invites her six little relatives to visit and to celebrate her cat's birthday. All arrive for a day of adventure as the children eagerly search Aunt Nina's country home for Fluffy.

Having decided it to stay home and forgo several suggested outings, the children proceed to ''unwrap'' a home for the cat - floor by floor. But alas, no Fluffy.

Finally at naptime, Aunt Nina pulls back the covers of her bed, and the children discover not only Fluffy but six new kittens - one for each nephew and niece. Over mouse cake and birthday song, the ecstatic children proclaim that Fluffy's birthday beats even their own.

Aunt Nina is a wonderful character, fully engaged with the children as she catches frogs in the pond and plays train and dress-up. She expresses an adult's delight with and appreciation for all the joy of children's natural spontaneity. Fluffy as the unexpected gift-giver is a happy reversal of the ''what's for me'' idea that often mars birthdays. The theme is beautifully supported by Aliki's colorful illustrations.