I was going to say the same suggestion as Sarah.

Have you got an ensuite, Sam? Maybe one of the boys could use that toilet so that they have their own separate toilets? Uno... maybe you could say to Mason: "Because you're such a big boy now, you get to use Mummy and Daddy's toilet!".

I'm the same as the others tho... haven't got to that stage yet so I probably have no idea what I am talking about