I don't see any reason not to let the kids swim. You can add the bleach in when they are done.

I would try brushing the stains after you add the chlorine to loosen up as much as possible and let the chlorine do its thing. Keep the chlorine level up and keep brushing if that looks like it is being effective. You can also look in the Stains threads for more info on what to do. If you don't see what you need, then post a question in that thread.

The baking soda you can also add after the kids are done swimming. The CYA you can do right away if you want. No need to do this in steps. The baking soda will dissolve quickly, the CYA will dissolve slowly.

Peter