Man, my kids grew up fast. Found some:
- camo hippers with size 7 bootfoot,
- neoprene stocking foot that are sz L but the sock looks like a size 5 (so maybe for an 8-10year old), and
- a Cabelas lightweight chest wader with felt-soled size 6 boot.

Free if you bring your young fisher to get them near Poulsbo (no freebie Craigslister scammers who take them for resale). I'd say they are all 8"s out of 10 as far as wear, maybe better, no leaks.