Well, if they're much past infancy, there's only so much that could be done until they're adults anyway. Afaik, the kind of hormonal treatments to cause growth work way less past the early years. After that, it tends to need surgical intervention to change, but that's just based on the last time I was reading up on it, which has been about a year at this point.

That being said, it's worth talking to their doctor because the underlying causes can cause other problems that would be better detected early.

It's a really simple thing to have checked, it's just measuring the penis and comparing that to charts. No trauma involved, no complicated procedure, and unless it does point to a formal diagnosis there's no further action needed.

It's one of those things where knowing can give everyone involved time to prepare for anything down the road.