Answer:
Canine children.
The more you add the less it weighs. What is it?
Who makes it, has no need of it. Who buys it, has no use for it. Who uses it, can't see it. What is it?
I am a red drum which sounds without being touched, and grows silent, when touched. What am I?
Flat as a leaf, round as a ring; have two eyes, can't see a thing. What am I?
I go in hard, come out soft. Blow me hard and I'll make a pop. What am I?