Duvet won't stay in cover - driving us mad

[kittlesticks]

On top of two under 3 year olds who sleep badly, we are cursed with the problem of our duvet never staying in the four corners of the duvet cover. We've got a king size duvet and bedding from the same shop, so everything matches but still the duvet slips in the cover.
Does anyone have any recommendations - I've seen things advertised but also seen some bad reviews.

Sew some large presstuds inside each corner of the duvet cover and on the corners of the duvet. Simply clip them together and unclip to wash!

Thank you, I will do that!

This happened to my daughter every day, so we got her a patterned duvet from M&S. I have been browsing at M&S and found this: www.marksandspencer.com/coverless-spot-10-5-tog-duvet-and-pillowcase/p/hbp60214042?intid=mobile_app_pdp_share @

I sewed a bright little ribbon loop into the corners of the cover and sewed a tiny strip of ribbon on to the duvet with a button attached.

That way the buttons dont go in the wash as often so don't tend to come loose/get damaged but if they do I just need to sew on a new button and because I used a bright colour they are easy to spot. Then I just turn the cover inside out, hook the buttons through the loops and then flip the cover over the duvet and the cover is changed and secure in seconds.

Didn't quite understand anyone's solution, I have the same issue, with only one of my child!! I honestly don't know what he does in his sleep, but every morning the duvet inside the cover is folded in itself. So annoying