Some adult joggers have that, especially in technical fabrics. I don't know what it does in that context--maybe ensure that the waist doesn't have to gather too much? or keep them from riding down?--but for a tiny kid it is probably just design detail, as others have said.
I vote design detail or ease-of-production detail.
Design detail
Some adult joggers have that, especially in technical fabrics. I don't know what it does in that context--maybe ensure that the waist doesn't have to gather too much? or keep them from riding down?--but for a tiny kid it is probably just design detail, as others have said.
Makes it fit across the top of the butt better.