for It's My Birthday, Too! by Lynne Jonell and Petra Mathers
It's Christopher's birthday, and everything is perfect. Except for one thing: his little brother, Robbie. Robbie thinks that it's his birthday, too, and he wants to come to Christopher's party! Christopher is sure that Robbie will wreck everything -- until Robbie comes up with an inventive way to share his brother's day. Simply told and illustrated with bright, childlike illustrations, this hilarious picture book hits the topic of sibling rivalry right on the head.
Publisher description retrieved from Google Books.