Having successfully (I think) winged my way through DD's third birthday party, held jointly with a friend, we now have a house full of presents, mostly still wrapped. Now, I'm wondering - when you have been given presents in person, and either you or your child (DD was too busy bouncing to personally greet ALL her guests) have said 'thank you' to either the parent or child giving (some of the guests were too busy rushing off to bounce to hand the presents over!) ... is it 'done' to send thank you notes, or have we done 'enough'? Complicating factor is that some of the presents became detached from their accompanying cards and we don't know who they're from ... but if thank yous are the way to go, I'm sure we can manage something.
I don't think I would expect a thank you note under the circumstances, but I'm not the most socially ept, and tend to get these things wrong.