My friend is 16 years old and has slight bow legs. He can't afford physiotherapy, but I've seen many exercises online that I want to share with him. I'm just not sure which are the best, or how many to do. I know he should strengthen his adductors, but which other muscles? What are your suggestions for exercises?
If your friend has genu varum, he needs to talk to a physical therapist to get an idea of how significant the problem is. I know of adults who squat and deadlift just fine with slight bowlegs, but in medical literature it's noted that genu varum conveys a higher rate of arthritis later in life.
It's just too difficult to say what's safe and what isn't with a condition like that because there's too much variability and their anatomy is a bit different.
A physical therapist can diagnose the extent of the issue and advise on exercises that won't make things worse. It's really worth the ~$100 USD.