If you were throwing a daytime party (birthday, baby shower, bbq on a summers day or whatever - that sort of thing) do you think you need to explicitly say that it's child free or should people assume it is unless they have received an explicit invitation for their children?
Random vote:
YABU - it's up to the party planner to specify its child free otherwise you should expect children to come with parents
YANBU - Guests should assume child free unless they are told otherwise.