thread It's not just about how likely the children are to spread it.
My kids are staying with my 75 year old mum and returning the kids will force myself to mix with her as she lives a few miles away and I will have to pick the kids up and drop them off. I'm going to work still and there is at least one person off with confirmed covid19.
permalink you need to hose them down with vodka before dropping them off

but your set up sounds like a case of "don't do this" either they don't go back, or you need a different set up... or a way to avoid mixing with your mum..