Do you think having antibiotics blocks a child's body from learning how to fight against the bacteria naturally?

Sometimes. That's one of the reasons we don't give antibiotics for all bacterial infections, only for ones likely to cause harm to the child.
Not really. Antibiotics are only of real need or benefit to treat problems the immune system won't fix. You would never omit antibiotics when a meningitis would otherwise kill the kid in days. You might for a middle ear infection that could self heal with immune system help in 6 -8 weeks, but would you really want them to be in pain that long.