Give a little boy some balls and he will happily play with them for hours.
You are welcome to take that line anyway your mind wishes to travel.
There is the safe, sanitised, blissfully naive path of thinking that the balls being referred to are the sporting kind. Tennis balls, footballs, basketballs, soccer balls, billiard balls……….
Or……
You can take the path that heads straight to the gutter and imagine that I was referring to the balls given to the male of the species homo sapiens through the wonders of the x and y chromosome combination. Yes, I am referring to testicles.
Either way, the little devils will happily play for hours with them.