Children in the US used to grow up racist, and thought that interracial relationships were immoral. Now, most young people don't see it as strange at all. They learned racism from the adults.
The best thing to do is to come out to children as young as possible, and ideally never be "in the closet" around them. Unfortunately, most women have a strong protective instinct, and want to shield them from anything that has the slightest chance of being a bad influence. So, it is generally hard to sell this idea to the mother.
My inexperienced advice is to ask the children to explain why cross dressing is bad. You can give examples, such as why women get to wear men's clothes and nobody cares. Hopefully, children don't have such strongly embedded biases, and can actually accept their own logical reasoning that there is really nothing inherently wrong with cross dressing, but that it is just unusual. Of course, I would also tell them that society is biased, and that it is OK if they don't feel comfortable sharing this with their friends, or perhaps that you don't want them sharing with their friends.
