If the gentleman were friendly and innocuous, I would just let him be. It is important to know the nature of the disruptions that this gentleman causes. If he accosts people or makes outbursts, I would attempt to make it clear to him that he is only welcome if he remains quiet and does not <do behaviors that bothers dancers>. Also make it clear that the child may observe, and move around the periphery of the hall, but <whatever she does that's disruptive> is not allowed, and if it happens, that they will be asked to -- and they will need to -- leave and NOT RETURN.