The chicken pox virus lies dormant in cells. When those cells get damaged they release the virus. If you're healthy and not stressed it doesn't matter. If you're run down in anyway you get shingles.
If you've had the chicken pox virus you're not at risk from someone having shingles. If you haven't had the chicken pox the person with shingles can give it to you. So you would catch chicken pox, not shingles.
So someone going to playgrouo with shingles deserves a kick in the bum! Seriously bad form.
I had shingles years ago and avoided a pregnant friend even though she had the chicken pox just in case.
If it is shingles there's a very good chance of every kid getting chicken pox in that group. Very selfish behaviour.