As Holden walks down Broadway, he is cheered by the sight of the family that has just come out of church with a little boy singing.
Holden is walking down Broadway for no reason, because he has not been there for years. He wants to get a hard to find record for Phoebe called "Little Shirley Beans." He notices a poor family that has just come out of church, including a little boy who is singing.
He had a pretty little voice, too. He was just singing for the hell of it, you could tell. (ch 16)
The little boy is about six years old, with his mother and father. No one pays any attention to the boy as he sings about catching “a body coming through the rye.”
Besides the reference to the catcher in the rye, this incident tells us a lot about Holden. He likes the little boy because he is genuine. He is just being himself, with nothing phony about him. Holden feels protective of him, and all of the little children he wants to save from the cruel adult world.