RR,
Hard to say. Younger kids can't really play that well together either. YT enjoy her time with the older cousin more than the younger cousin although the younger cousin is more keen to play with her. However, they often fought over things. The older cousin like to teach her how to play things and explain things on TV to her. So a big gap is not necessarily bad. They tend to be more understanding at an older age. If not, whole day they just fight. Last time my cousins all much older than me but I actually play better with them than my own sis who is 2 years younger. In fact, I fought with my sis so much she wouldn't even call me "sis", to this day, she called me by name! It was after we left my auntie's house and stayed with my parents and only left the two of us then our relationship got a bit better towards our teenage years. So in my opinion, big gap better. Can encourage the kids to play their big sis/bro role.