it should be half-sies or halfy halfy = to share in half or halfsie halfsie to share half and half. basically it's just an informal often childlike way of speaking where the child puts on an 'es' or 'ies' onto words that do not usually require them; children are still developing listening and grammar skills. A few [very few] of these children trying to speak words have come to be used in general conversation. You should not dwell on trying the learn the very few that may exist.