Hi! I am an "older" mom I have a 19yold girl, 17yold girl, and a 13yold boy. I always made sure the girls especially knew that they were not a package deal! Sometimes one would be invited to a birthday party, and the other one would want to go, or ask for a treat bag also, when we picked up! It is important that children have their own identity socially. With age becomes different experiences, I would leave your younger one with a sitter because he would also enjoy himself more at home getting one on one attention with a sitter then sitting at a table being 2! I tried to make special time for each of them alone when possible, like maybe a day out with mom or dad with your 4yold and then another time with just your 2yold. It helps to prepare them for social life at school
later! Good Luck! Sounds like you are a very caring Mom!