Due to a very long story, I was recently up in my parents' attic in Florida, digging through some old boxes of my books. My main goal was to rescue a few old copies of my Baby-Sitters Club books, but I stumbled on some old favorites as well, including:
The Kid in the Red Jacket
Ramona Quimby, Age 8
Katie the Pest
The Boxcar Children
I loved, loved, loved books with multiple children -- whether they were all main characters, like in Boxcar Children, or just the foil, as in Katie the Pest. Living with several siblings leaves you predisposed towards books like this, I guess.