Please don't take this wrong, it's not meant to upset. BUT, STEPFATHER has chosen to be the father figure to these children. He's made that choice, not them. If he has the time to interact with "his" son, he needs to make the time to help with "your" children as well.

Your children see their stepbrother getting to do things, why can't they?

As someone else said, try signing your son up with a friend and ask the other parents to share carpooling.

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