You should be ok with Calpol, just be careful to follow the instructions on the label (everyone should do that, diabetes or no). The piriton is a bit more of a trouble, i'km sure it's ok to give people with diabetes but i'm not sure about five year olds. Ask at your local pharmacy they'll know, or at least have a BNF C to hand. It's probably ok, but i'm not 100% sure. If you want to use something perfectly safe i's recommend calomine lotion or ointment, that's soothing and cooling when you apply it to bites and make them less itichy, my parents swore by it when we were kids. My brother still has horrible problems with midge and mosquito bites. You could also, by the same token, try menthol in aqueous cream, but you might not want your child to smell like cough mixture! Hehehe, i quite like the smell myself.