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Camofire.com often has youth size clothing and rain gear and I have had great luck with it. Warm, quite and water resistant. Both my boys have used them for a couple years now with no complaint 8/10 year olds. Duck, deer and elk on the west side. I believe it is lucky bums brand.
I'd put the money in footwear first and scrimp on the rest if necessary.
Bad boots equal bad times. My experiences of hunting and fishing as a youth were marred with the memories of cold feet, blisters, etc. The worse memory was the few times I was willing to try ice fishing with my feet freezing constantly. I eventually opted out of the ice fishing expeditions because of this. For youth hunting clothing you might try the local thrift stores, they often have children's hunting clothes in stock. Kids that young will outgrow their clothing very quickly. We passed them down from kid to kid and shared with other families.