AKW,
Wait your son is older, then you will think about what class you want to send him. Yes, my daughter is happy for attending different classes and I understand that kids can pick up faster when they are young, so I want her to explore whatever I can afford then narrow down what she really like when she is older. I also think about Kung-ku, but for girls...may be for short while for learning the basic. In fact, I think gymnastic may be better and I have put her in drop in class before and she has lots of fun.
Learning should be fun and I will only let her go if she likes it. Swimming is the best as I want her to work as a life guard in colleague and earn some pocket money by herself..hehe.!
Music instrument...I have no talent on music as well as my husband, but if she likes it, then we may try. It just like learning Chinese, I ask her if she wants to go, never force her to go.
Yes, I heard in States medical is very expensive but I didnt think it is so bad! So, it is still very cheap in HK compare with States.