BACKGROUND: New estate, open plan, we are HA and have a garden - paid for (and maintained
) by HA and not community. Its off the road, behind our flats and bordered by car parks. We have sheds and washing lines in there so obviously ours iyswim. You have to actually come off the street and take a longer route to past through it. There is 2 blocks and 4 flats in each.
Lot's of issues with noise/ damage etc and we have begged HA for it to be fenced off and finally after 4 years we have fencing - well its the metal fencing found around parks iyswim?
Yesterday we had visitors and they went out to play in the garden and asked if a friend of all there's who lives on the street could also come in and play. I said yes, but just him, and they could go out to park over the road if they wanted to play in group iyswim? They asked neighbours DD (7) if she wanted to play too but she isn't allowed out/ won't play with other children.
Neighbour came out and told DS he couldn't just invite a whole load of people to play as it isn't just his garden. It was 1!!! 
AIBU to think that although it's a shared garden that doesn't mean that DS can't use it when he has friends over or invite a friend in to play?
BTW her DH works nights and so I already put so many limitations on them during weekedays to keep noise to a minimum - so I'm not a selfish cow I promise!