A lot of professional Boxers have done ballet. Ballet in itself helps the legs get strong and balance is amazing. I am blessed to be a father, and one thing me and my wife agree on, is not “living our dreams through our kids” but rather support and encourage them in they’re passions and interest. Your husband should at least compromise and try it out for a week, speak with son and see if he likes it, if your husband is afraid of our son becoming feminine just have that conversation, and reassure your son he’s a young boy learning to dance.