The boy living on the streets, seeking companionship and the need to protect (possibly the way he wasn’t), jealousy of a well looked after cat with a home, the use of crumbled up (thrown away) paper at the beginning and end of the book.
“There was not a boy on the wharf Johnny did not know. He had made friends with some and enemies of others, and had played or fought with all of them. […] Seemingly in one month he had become a stranger, an outcast on Hancock’s wharf. He was maimed and they were whole.”
The Mouth-Organ Boys. This one was about a boy who wanted to belong to a group so badly that he couldn’t see the bad way they treated him. He can’t see that his mother is already giving him all she can and all he needs.