DH's is 50 this year. We're planning a big party and BBQ. Will be about 90 people including children. Last year we packed away the toys in boxes in DS's room just to make more room for the party - normally he uses the conservatory as his playroom but we needed it empty for the party.
Various small children arrived and proceeded to play the role of small tornadoes! DH were busy cooking, serving and pouring drinks. We didn't notice quite what was happening. Two of the little cherubs had taken water out of the pond with a watering can to water the grass 
. They had smashed up 2 water lillies that I had hoped would flower that summer. They managed to push the liner down so that the water leaked out. And when I went up to DS's room I found all the toys had been taken out and mixed up all the floor and the bed. And a lot of them had taken a trip to the garden and were scattered everywhere including in the big pond that was too deep to get them out. DS was really upset when he saw it.
It took a week to get everything sorted and find all the missing bits.
I want children to be able to play with toys - that's the point of them but I am realising that the assumptions I made about children - that they have been taught to behave with respect towards other people's homes and possessions may not always be correct 