Neighbours children cracked our windscreen

You don't have any evidence. I don't think a modern sliotar could do any damage to a modern windscreen, especially not take a chip out of it, and especially if it ricocheted off a wall after being hit by a child.

Might be covered for free under your insurance policy also by the way.

Yes, it would be unreasonable in my view.

Stone chips are caused by a combination of the velocity of the stone and the velocity of the car.

In this case the car was stationary.

I don't think the chip from a wall would have enough force to chip the windscreen, without any evidence of the kids next door causing the damage yiu don't have much of a case but if you have windscreen cover on your insurance it probably won't cost anything to get it fixed

Ordinary principles of negligence apply. If you give your 13-year old a gun, say, or the keys to the car, or otherwise put in him in a situation that a child can't be expected to handle competently and responsibly, and damage is foreseeable, and damage results, you're on the hook. Same may go, depending on the circumstances, if your child is in that situation and you do nothing about it (as opposed to having put him in that situation yourself).

But "child kicks ball, ball breaks window" and similar common accidents involving children are very much not that situation.