I am Going! by Mo Willems

From chapters.ca:
When Piggie tells Elephant, "I am going," you can imagine the thoughts that run through Elephant's head. Elephant, after all, sees everything in the darkest possible light. "What about me?" Elephant whines tearfully. "Who will I skip with? Who will I play ping pong with? Who will I wear a silly hat with?" Piggie remains resolute. She is going. Elephant declares that he will go, too. But that doesn't faze Piggie. Mo Willems, a master at comic pacing, delivers another perfectly delightful Elephant and Piggie schtick that will have kids laughing as they learn to read.