My biggest 'pet hate' with regard to other people giving my kids food is when it's given around meal times as I know they won't eat their dinner/lunch if they have just had a sweet. So the treat itself doesn't actually worry me that much (provided it's seen as a special thing, not an everyday thing) but god it annoys me if it's given before healthy food! My kids aren't particularly food orientated so I find they need to be peckish to eat their main meals so we limit snacks during the day. Hard work when some random person offers them an ice-cream at 4pm!