You did the right thing all throughout the situation. Her "feelings" on the family don't matter except in the fact that she's being a bully and was out of line. She doesn't have the authority or the right to exclude a boy from a team event just because she dislikes the parents for no real reason other than being racist.
I would remain polite to her and keep it professional. Respond with, "I'm sorry that you're upset but this is a team event. Let's get on with the business of planning the team party. If you don't feel comfortable including all the children and their families on the team then feel free to step down and I'll gladly take over."