is this petty? what would you do?

so me and my x share a son and I have full custody...no issues there...my problem is my x keeps things and refuses to give them back. diapers and wipes were one thing but money get a tight and he has not been made to pay child support...i pay for everything and I can't afford what he's been doing. if I pack my son extra clothes he keeps them so I stopped...my son likes to bring toys/blankets/things that make him happy to his dads to help him sleep but I never get them back...he has a hat my mum got him for his birthday that's very special to him and his dad refuses to give it back...so now all I send him in in a single outfit because he's kept so much clothing he should have lots to dress him in.. but my son tells me he doesn't get any pjs or his clothes changed while there...i want what's best for my boy but I can't afford to buy him a new wardrobe all the time...its now at the point he's keeping his coats or stupid things like underware and socks...i really don't know what to do as I have 2 other kids...my husband is trying his best to provide for us as I'm not able to work as I'm about ready to pop with our third and high risk and we have been stretched to the max financially due to this...we were well off before when I was working but due to court and my x wanting to bleed me out to get what he wants out of court were super into debt (he's on welfare and has court paid for where I have to pay out of pocket)