Depends on the child, venue and what the party is.

Liebling has insisted I stay until age 6, but many parents have told me I can go before that.

At leisure centres etc they have enough staff so I can leave, at people's homes I ask if they want a hand.

If an entertainer is provided, I am less likely to be needed. If it's the sort of party I do, an extra eye for the activities is usually welcome so I can serve up hot food too.

So no hard and fast ettiquette. I would say you pay for the invitees, not any tagalongs though.