my sister does that a lot. she will even show him the stuff he stole.

but i guess it takes time. nowadays i try a modified carrot n stick method on him to retrieve the stuff he stole. seems to work, coz in the past, he won't surrender it. he'll just shred the loot to pieces.

so when he grabs a slipper and won't let go, we bring him into a room and close the door. i'll ask my mum n sister to talk excitedly n loudly outside the room, so he'll want to go out to play (they're his fac playmates).

then i open the door slightly to tempt him. he comes to the door n i try to take slipper away. if he won't let go, i close the door and smack him on his butt (gently of course). then he'll walk away from door with the slipper.
so i repeat the process. and when i see him put down the slipper, i open the door wide. if he grabs the slipper to run towards the door, i close door again. eventually, he gets the idea tt he can only get out if he surrenders his loot.

and this is becoming easier as time goes by. he takes less than 5 minutes to surrender slippers now.