Sizing?!?!?!?!?!?!?!

• I got Mica socks today. He's a 10 1/2 in shoe size. It's so confusing trying to get socks for his size.
• I ended up getting a 9 to 2 1/2 size. They switch from kid sizing to adult sizing.
• I turned around and looked at underwear, and got all the more confused! In some brands they go from extra small to extra large and in other brands they have numbers for sizing. In the number ones they have size 4-6 and 6-8. Well if 4-6 is getting kind of tight, I have to move up to the next size that will be swimming on him. Where is size 5?
• I think it's incredibly confusing!