I'm so devastated for my son

[Ktownmatti]

It's nice that you don't want to upset your son and protect his innocence. However, just like any other problem in life ignoring the problem doesn't help one bit. Especially in this case when the earlier you address the problem the greater the likelihood of a favourable outcome.

90 percent of all men who take propecia will experience no further hair loss. There will likely be some much better treatments/therapies in the next several years so propecia is not a life long sentance.

IMO you have two choices:

Be proactive and upset him a little now and attempt to solve he problem or;

Put your heads in the sand and have him be VERY upset in a couple years when it's too late or him to have a full head of hair.