re: chronically sick toddler

Everyone has strep bacteria in their throat.

Here's a quote -
It is much more likely that the person suffering from chronic strep throat and sore throat has a neuroimmune system which is somewhat suppressed, depressed, or otherwise functioning at less than optimal capacity due to other chronic reasons.

Antibiotics suppress the immune system exactly as described. Just one 'wrong' prescription of antibiotics is enough to start this whole vicious cycle that he's going through, so it is a possibility.