If a kids going to be ill from eating n then bouncing about it happens straight away. Its illogical that itd happen later I think... n I dunno about other ppls experiences but most of the parties I went to as a kid had either cold stuff like sausages on a stick, sandwiches n chrisps to eat, or fast food, neither of which is likely to be contaminated with anything nasty- I mean it all comes straight out of packets anyway. Just train your kid not to pick food up off the floor or anything gross n they should be fineeee.