What Causes Redness Of Cheeks After Taking Neproxen In Children?

Hi my son is two and a half and he bit half a neproxan that was fully 500mg and swallowed it. I was told by a family friend pharmacist that i should wait one to three hours for symptoms and the next day his cheeks were getting red as if he had a reaction. And his right side of the cheek is more red than left otherwise he is acting completey normal and he s not puking or anything. hes eating properly too. Please let me know if the redness is not a good sign?