A Letter to Amy by Ezra Jack Keats, 1968.

Peter wants to invite Amy to his birthday party, even though most of the other kids at his party will be boys. He has a crush on Amy and wants to mail her invitation as a special surprise.

After a couple of false starts, in which Peter almost forgets to tell Amy the time of his party and almost forgets to put a stamp on the envelope, Peter sets out to mail the letter. It’s a rainy, windy day, and the letter gets away from him.

Peter chases the letter and ends up colliding with Amy. He mails the letter quickly so that Amy won’t see that it’s for her and spoil the surprise, but Amy runs away, crying because she fell down.

Peter worries that Amy will be too hurt and angry that he ran into her and knocked her down to come to his party, but things still work out well.

This is a fun slice-of-life story about the awkwardness of first crushes.

The book is available to borrow for free online through Internet Archive.