I have a question about kid sizing. Up until now, my son was wearing 4T, so I would buy him 4T pants and shirts. I want to buy him clothes in the next size, but I saw the shirts are size S (which is supposed to be for 5-6) and the pants are either size 5 or size 6. Does that mean he would go through two different pant sizes for the same shirt? It seems odd to me they don't pair up like they did with the smaller sizing.