There are so many variables here, and this isn’t much of a case history to work with.
Number 1: We don’t know, precisely, how it spreads. We have really good ideas on the transmission, but this still such a new disease that scientists are still working it out. We also don’t know what viral load is needed to trigger the response in the body.
2: We don’t know your health situations. Blood type, fitness, etc. Those have some correlation to outcomes, although the causality is not understood nor confirmed.
3: What was your exposure level to them? That is not listed here.
4: Is it possible that you and/or your son were the original asymptotic spreaders for your household? If so, you would both test negative in the nasopharyngeal swab test after your immune system handled it.
5: How were each of you tested? The different tests have different failure rates. It is not inconceivable that you fell into that area and none of you were actually positive. I am NOT saying this is the case, but it is not unheard of.