Do they put helium in soccer balls?

Answer 1

No, soccer balls are filled with ordinary air If they were filled with helium, they would float into the sky
Helium filled soccer balls would certainly not "fly into the sky"! The difference in mass of an air filled ball and one filled with helium would be but a few grams! But the helium (having a much smaller molecule than those that comprise air) would leak out of the bladder more quickly. In addition Helium is much more expensive than compressed air.

Answer 2

Yes. They have special structures inside to keep them spherical but they are full of air.

Answer 3

No, Soccer balls contain oxygen and carbon dioxide. If they contained helium they would most likely float away.

Answer 4

No.