From what I have read, food divides up into "halal" (acceptable to Muslim dietary laws) and "haram" (unacceptable) so it is not a case of looking out for specifically "halal meat".
M0nica, , I appreciate what you say but if anybody, 4 or 40 is of a religion or cultural background which precludes a food type ("haram") I will respect that just as I would expect his primary school to respect ethnic differences.
So while we and his Scottish Greatgranny may tuck into what pleases us, I would not dream of giving him sausages, burgers, jelly and ice cream -all of which my DGSs would have loved, if that is not suitable. To me this 4 year old's needs must be taken into consideration, just as if he suffered from coeliac disease, or was diabetic, so I don't actually agree with your final sentence that you would "expect a 4 year old to eat the same food as adults and not require separate catering".
What I am realising, though, is how European, white, middle class, dare I say "English" the majority of members must be for nobody to say what they give their 4year old Muslim/mixed race/whatever DGC to eat!
(I realise I expressed myself badly, perhaps making it look as if DH's cousin as well as the little boy was Muslim, but he is the son of her late husband's daughter from his first marriage, also Scottish, but married to a N African. Cousin is on half term "Granny duty" and the little boy and his family live just 12 or so miles away from us, so a good opportunity for DH and cousin to meet up. )
Sorry about that.