Shoot, what was the book series about finding an alien in your cereal? It was called something like "there's an alien in my cereal!" No! That's somehow unrelated. I was thinking of Aliens for Breakfast by Jonathan Etra and Stephanie Spinner:
Image: A children's book cover with cute cartoon art of a boy with glasses looking surprised by a tiny insectile being standing on his box of Alien Crisp cereal. Above the title (Aliens for Breakfast) is the smaller text "Richard doesn't know it yet, but he has only five days to save the world!"
In the top-right corner is a logo that reads A Stepping Stone Book, and in the bottom-right corner is the two authors' names, and "Illustrated by Steve Björkman".

GET OUT OF HERE! THEY'RE COMING! TELL MY WIFE I LOVED YOU

Don't forget about Have Space Suit, Will Travel