My nephew is stealing money

What would you do when you find out your child (you're his uncle, dad, granddad, mother, grandmother, whatever) steals your money? He keeps stealing. You feel like you've done everything you could to parent him but nothing changes. But you know you cannot give up.

He's a kid, 1st or 2nd grade. He uses the money for toys and play (video games), buy stuff for himself and his friends (the worst part I think).

You're his dad, you've failed to parent him from the beginning but how'd you do to fix that?

You're his uncle, grandmother how'd you do to fix what's been done and do what others cannot?

I really need serious advises, I'm his uncle.