Our daughter told everyone in her preschool that she had two mummies and daddies so it was good the staff knew so they could explain to the other children what she meant. They simply told them her birth mummy and daddy couldn't look after her so she was now with us and as children do they just all accepted this. I don't think it is necessary to make a big thing about it but I think you should make the staff aware then if they do mention any problems that would be the time to go into more detail if necessary.