Inspiration for jumper or cardigan if cut down the middle? And I might cut up and lengthen the inner sleeve seam, this creating more of a side seam at the same time so it's not quite so revealing on the sides.
It honestly looks like a diaper onesie combo. Imagine how when it gets wet it's going to sag in the back than it already does because of so much fabric bunched up there. Totally looks like she's got a full diaper on under it