What kind of clothes should I dress him in?

I have a son in the lower grades of elementary school, and he has gained a lot of weight lately, so it is difficult for him to find clothes.

Especially since my belly is too big, if I get the length fitted, the fit is tight, and if I get the fit fitted, the length is long.

I don't know how to dress it.

How should I dress someone with a protruding belly like this?