I hate sizing on socks because the "right" size in big boy socks are HUGE on little feet.

For a while, I would look in the toddler section and get the ones that were extra-large, possibly labeled age 3 - 5. Don't remember what brand. Those worked for the interim.

Now Mark can wear those 9 - 2.5 socks pretty well because he is in a size 12 shoe. They get pretty snug at the top range as well.

Keegan wears a size 8.5-9 and wears the 2T-4T socks from Kohl's - They are white with grey or navy toe and heel.

Bryce and Owen are both in the 9-2.5 size.

Bryce is actually in a 2.5 but the size up are still huge right now.