R.J.
What you want are $1 plastic rain ponchos. Cut the adult ones to fit.
Alternatively... Garbage bags with holes cut for head & arms.
Happy decorating!!!
And as a mom whose kid comes back stained all the time, THANKS!!! Yay! Minimized stains! (there will always be ONE kid, at least, that the laws of gravity work differently for... Or who intentionally gets stuff on them.)