How to stop DS from pulling sheet off cot mattress?

[LaDameAuxLicornes]

Does anyone have any tips on how to stop DS (8 months) from pulling the fitted sheet off his travel cot mattress when he's put down? He's discovered that he can yank at it and pull it up at the side and it eventually it starts coming right off at the corners. He's also very excited to discover that he can pretty much roll himself up in the cot mattress by using this trick.

I'm concerned about it from a safety point of view (smothering), and it's also really disruptive to bedtime and nap time because he arses around with it instead of going to sleep and if I have to keep coming in to take it away from him and redress the bed he gets very overexcited and thinks it's playtime. No idea how to stop him doing it.

Could you get some of these mattress straps not sure if they would be short enough for a cot mattress, but might hold the sheet in place.

My 7-month-old does this with flat sheets, but can't manage it with fitted sheets because the elastic holds them in place. I'm impressed that your son is able to manage fitted sheets too No suggestions, just following to take advantage of the advice!

Can you sew some ties - maybe three sets? And then tie tightly underneath? Or some Velcro under the mattress and then strips on the sheet?

or a piece of material at the back to make the sheet like an envelope so the backing sheet will keep the front sheet in place

YouWhoNeverArrived where are your fitted sheets from? Maybe mine are just too big for the mattress, though I thought travel cots were one standard size. My sheets are just cheapie ones from ebay, though.

Think mattress straps would be too big, unfortunately. Velcro is a possibility, thanks. isseywithcats I'm struggling to picture how I would do that - do you mean put two sheets on, one on each side of the mattress? Or something else?