I think it's out of order for people to just assume that children are invited everywhere the parent are.
We've got 2 children (10 & 7) and always make it clear when we're inviting people round (whether or not they have children) if it will be a grown up evening or not (deliberately not saying adult as that implies an entirely different sort of party :wink: )
We'd assume that any evening invitation was for adults unless childres were specifically invited.
I don't want to sound like a complete killjoy, I love partys/events/barbecues/days out with children, they're usually hugely fun but there is a need for grown up time.