I don't know exactly what "activities" you are talking about. The OP asked about ballroom dancing.
If a very young child asks their parents why two men are dancing together (and I doubt that they would) all the parent has to say is they enjoy dancing. As for an older child, unless they are VERY sheltered, they already know and wouldn't ask.
IMO, a good parent would have an appropriate answer for any age child.
These children are going to grow up to be part of this world, and in this world there are many people who do things differently. IMO, the younger they learn this, the better.
Men dance together, women dance together, groups of people dance together! I really don't think children care at all! I know I don't!