If he can't find one that's small enough, I am going to be cutting my binder down sometime between Thursday and this weekend to make it smaller and will be posting directions on how to do it. I don't think it'll be too hard for someone to alter it to be smaller. And, he can always just hem the extra in so it can be let out later once he grows more.
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Also, if he can't get a tape measure, he can just use something else that can go around his chest that's not stretchy (like a yarn is stretchy, so something like a wire or twine would be better), and then just measure the amount used with a straight ruler.