Blanket won't stay on!

[Kanny08]

Hi my son is 4 years old and in his own room. When he's sleeping he moves a lot so his duvet comes off and then he calls for me to put it back on him. How cn I teach him to put it back himself at night when it comes off.? Thanks

Hate this. I’ve replaced the duvet with blankets and tuck them in really tightly. It’s the only thing that works.