I am allergic to all tree fruit. Started as OAS, turned into anaphylaxis new year this year after eating a vegan mince pie (also anaphylactic too all dairy, hence the vegan mince pie).
I landed in hospital within an hour of eating it, and we eventually figured it was the apple in the pie.
If you have a guest child over, you cater for them. If you have you own fussy child who then has food or meal issues, one day (for one guest) won;t hurt them, nor you. However, trying to get picky over 'does he REALLY have an allergy, surely one piece of fruit can;t hurt.....well, it can!
There are other snacks you can offer that are not biscuits.....altho I concede biscuits are an easy option, and probably the favoured option with children.
Gotta say tho.....why would fruit not ruin your DS2's your appetite for dinner and yet a biscuit will?? My own DS2 is a swine for dinner if he eats ANY snack, regardless of whether it is fruit or biscuits.
Oh, and as an added going on your very last comment...
Allergies can develop at any time....just because they haven;t mentioned before doesn;t mean they are any less real. Hormones and puberty can be triggers, so what before might have been a mild and annoying tingle with some fruit may NOW be a full on reaction.