Where I live it is foggy and will be for the next month or so. About 8 degrees. DS (11) wants a birthday party. I have said we will have to wait and see. There's no way we can invite kids inside but we live in an apartment block and share a garden with the neighbouring block. If we stand at our door, we can see the outline of the end of the garden. It's not long, nor wide, just foggy! There's. 6x6 patch of grass which can't be used as it's damp and muddy and a path (1m wide) leading from our front door, past the other house to the road.
There are two 11 year olds, one 8, one 7, two 3 who all play together in the garden. If I were to invite a friend from class that would be another 10 and 7 year old. (Allowed, we can meet up to 10 people.)
Beyond serving cake, what could you do to make it a bit more "party-like"?