OK, I am quite amused myself by the notion that some animals are more unclean, or for that matter sacred, than others.
However, that's not really the point - if my Muslim CM pops round with her kids, I don't dosh out gelatine based sweets, because that would be rude & inconsiderate.
For that matter, we're unlikely to have such sweets - I'm veggie, I don't buy 'em - but the dc have a tin into which all sweets go - so anything given out at school/parties/by relatives might contain gelatine. Which doesn't bother me personally, any more than the 1000s of insect bits in my tomato ketchup.
But 'not eating sweets' & 'not eating sweets which include gelatine' really are not such bizarre & isolated concepts as some of you seem to think.
In ds's class, there are about 10 Muslims, for a start.
As for objecting to fruit, OK, perhaps some parents do. But I imagine it's rarer. If I'm wrong about that, fair enough, I wouldn't send fruit either.
Still don't get why giving out sweets is such an unmissable feature of anyone's birthday.