Wall-e Halloween costume DIY change of plans

So, it's a miracle but I actually got my son to wear a box! (this is my daughter in the pic) SO I will be doing a box version of the costume! Yay for Jais!! The box I found is 20x18. I cut a hole in the top middle and tried it on until it fit over head comfortably, eyeballed where the arms should go, and cut those a comfortable size...