Why can't my children actually play nicely together?

[Bert2e]

It's not as if they're toddlers, they are 8 and 11, but the older ones spends his time winding his brother up and the younger one just screeches all the time at his brother. Today we were meant to be going out but as their behaviour was so bad (including hitting and kicking) I've cancelled the trip so now I'm stuck in with them which is more of a punishment to me than them. Tell it it will get better - or do I just need to have them in separate holiday clubs all summer for the rest of the holidays so that I don't go mad? It's times like this that I dread spending time with them and can't wait for school to restart :-(

Have no advice i'm afraid, but definite sympathies. My two (ds is 11 and dd is 4) i'm finding it really hard to find things to do that interest them both. They then succeed in winding each other up and dd has a foul temper and is driving me mad as she is so demanding. Is your older dc about to change schools? My ds is definitely behaving differently because he keeps having a few fears about the prospect of high school.