Hi Jessica, I have heard many stories over the years about this from other poly* families about this exact situation. The one consistent outcome is always that children will accept you for who you are so long as you yourself are comfortable with it. You are their example and they sense things in you better than you realise and care more about you than anyone can.
The surprise has never been from the children but from other adults behaviour. For example, I had a friend whose children were in school and the children were fine with their parents choices. One of the children's friends happen to mention to their mother that my friend's children had more than one mother. That parent wasn't so respectful and attempted to limit their children's contact with their friends. The other parent's children got upset and asked why they were being limited from contact with their friends if they had done nothing wrong. The children were the smart ones! The other parents were forced to rationalise their choices to their children which brought about an awakening of sorts and eventually everything went back to normal.