Oh we have a friend with kids around the same age. Every time we visit it’s the same story. My friend tries to invite a friend of hers (the little girl) over at the same time then everyone gets to play. But obviously that can’t happen every time so even just distracting her and doing something special that only the girls are allowed to do. That way she feels special too and she’s not excluded.

The boys should learn to be tolerant and be able to adjust their games to suite all included. Your son has a little sister, he needs to accept that and be able to adjust accordingly

I was in the same situation with my two kids. I found the eldest (my boy) would have a friend over and they’d be on the trampoline and the younger (my girl) would get on the elder two had to stop because the younger was too small. So they’d let her have the trampoline and go play lego. Then the youngest would get sick of the trampoline since the boys weren’t on it any more and she’d go find them and start to grab at their lego and break their creations tat they had put such creativity and thought into. My conclusion: she had to learn that this is not your friend, this is your brother’s friend – she needed to do something else while they were playing, it’s just wasn’t fair on the boys.