Bedsheets - poly cotton or 100% cotton for childs bed?

[lovefairylights]

Does it make a difference on sheets/pillowcases? Found some in the right colours to match the duvet sets but not sure what I am getting by spending a few pounds more for it to be 100% cotton.
At the back of my mind is a voice saying go for 100% cotton - as natural a material as possible, but does it make a difference on bedding?
(We've ordered 2 duvet sets - one is 100% cotton, the other is a 50/50 poly cotton mix, but not arrived yet so I can't do the touch/feel test)
I guess with children's bedding we need something that will withstand significant washing. Is it the poly/cotton or the cotton stuff that is more likely to go bobbly?
Thanks

It's the poly/cotton that goes bobbly. All our bedding is 100% cotton, has a much nicer feel to me and I usually buy it in the sales.

I've got a mix for duvet covers and pillowcases but all bottom sheets are cotton.

My DCs love brushed cotton sheets in the winter, very cosy.