I'm sure we're not the first or last parents to do this to a kid.
Sometimes a kid isn't ready/interested in potty training for whatever reason, but still likes to take his pants and diaper off and make a mess. This is what we do if he needs to be put in his room for a nap. Please, no comments on how it's time to potty train him... I don't want to discuss it.
a toddler who keeps taking his pants off
zippered, footed pajamas
Step 1: Cut Off Pajama Feet
Find the elastic at the heels of the pajamas. You'll want to cut below that and below the end of the zipper. Cut off the feet of the pajamas. The fleece doesn't need finishing at the edges; it doesn't unravel.
Step 2: Put Pajamas on Toddler
Put the pajamas on your toddler, but backwards. Zip the zipper in the back. That way, he can't reach it to take them off.
Now he can be put down for a nap without you worrying about washing all his blankets, pillows, and sheets later. :)