The 7 year old is having a friend over for a sleepover, while the 9 year old is off to Granny and Grandad's (she can get a bit anxious when her little sister has people over).
I'll roll out a pizza base for them, set out all the toppings, and let them make their own creations.
Once they have eaten I'll make pizzas with whatever is left over for MrRed5 and myself.