Thanks for the feedback. A marquee in the garden is out, it's tiny, closest to a marque would be the 3 man tent!
Toilets, hmm, I am considering the folding potty in case of desperation or failing that a grown up to escort anyone in need back to the house.
I will say on the invitations that it is in the park, summer birthday parties are most often in the park round here.
There will be a treasure hunt, cardboard castle and a few running around games.
I've thought about bringing hot drinks in thermos pots, food, cake, a picnic table, table cloth, balloons, bunting, decorations. I've picked my spot near a couple of evergreen trees for grown ups to shelter under.
I have decided that in case of snow, some changes to games and bum board races to be held. Might need another bum board or will the tea tray do?
I guess I'll need a couple of grown up helpers and am thinking that if we can organise a quick pack up while kids have a few minutes in the playground, we might be able to end at home. Just need to recruit some grown ups. Getting stuff to a hall and back is probably more complicated.