Where can I find good shoes for my son ?.? PLEASE !!! HELP !!!?

My son is 6 and he was diagnosed with Type 1 Diabetes at 4 ... He is also flat footed ... I seriously worry about him every day, so any thing I can do to improve his well being I will ... So I was wondering if any one might know the best place to get him some good supportive shoes ... I have tried Stride Rite and so far so good but that won't last forever, they only sell kid shoes ... PLEASE AND THANK YOU !!!!!