The book had a light pink cover, if I remember correctly.
There's a young girl who makes friends with a very adorable smaller kid on the bus whose name is Sam (I think). There's a new boy in her class that she dislikes immensely. The protagonist invites all of her friends over to her house for a sleep over where they take silly photos in their pajamas. She's bringing the photos to school to hand out to her friends when she bumps into Sam on the bus and they accidentally swap folders. Sam gives his folder to his older brother (who turns out to be the boy our protagonist dislikes) to give to our protagonist. Instead Older Bro shows the photos to everyone. In retaliation, our protagonist teams up with her friends and go to the Older Bro's mother, explain what happened, and ask for embarrassing baby photos of him. They show these to their class as well and the conflict is resolved.
There's a young girl who makes friends with a very adorable smaller kid on the bus whose name is Sam (I think). There's a new boy in her class that she dislikes immensely. The protagonist invites all of her friends over to her house for a sleep over where they take silly photos in their pajamas. She's bringing the photos to school to hand out to her friends when she bumps into Sam on the bus and they accidentally swap folders. Sam gives his folder to his older brother (who turns out to be the boy our protagonist dislikes) to give to our protagonist. Instead Older Bro shows the photos to everyone. In retaliation, our protagonist teams up with her friends and go to the Older Bro's mother, explain what happened, and ask for embarrassing baby photos of him. They show these to their class as well and the conflict is resolved.