Apostrophe usage?

I've written:

Special offer: For a limited period (to celebrate the launch of our
saunas in Chalet Harriet 1 & 2) we are offering our free children's
discounts on both chalets for 15th December and 22nd December.

I particularly want to know if it's "childrens" or "children's" (with or without the apostrophe) and if the brackets above work? Thanks