You know, they just might. I have a 4-5t boy but he is a skinny guy so these are a tad bit to big. But if your guy is not so thin then they might fit better.
If he is on the slimmer side they just might. My older son is a 8/10 and these are a little tight. I believe the number size is 5/6 small but if your boy isn't a chuncky monkey like mine then they might fit.