Kids have a thing for balls. Small balls.
Just place ginormous amount of balls in a room and kids are sold. They will be playing silly, with all the balls at hand, throwing balls at each other, dogding or simply dive in. Parents can sit back and relax.
Now, where were all these balls when I was a kiddo?
As my dad used to say, to entertain Ah Boy, get a box and place me in there. I was happy with this arrangement, it seemed :p