Get cloth nappies
Sounds like PICA. My daughter has is. She chews and ingests non edible things. It’s part of autism as well as a vitamin deficiency. I just had her bloodwork done and everything was normal so for her it’s just part of the autism.
I had this problem years ago with my son & we solved the issue with putting him in a one piece pj that zips in the back & has snaps at the back of the neck. They are called LittleSleeperKeepers, you can find them online. They are expensive, but worth the peace of mind.
They have them for older kids ?