Always rinse after a swim, especially in public pool.
You will want to invest in some moisturizers, too--whether it be in the shower or out. Lastly, there are rinses for hair that get chlorine chemicals out of your child's hair. You don't have to use those all the time, but maybe once a week or every other, just to get it clean. As a kid, i rinsed after a swim, sometimes washed depending on how dry my skin felt, and I rarely washed my hair....it was so baby fine that the chemicals and letting it air dry actually "thickened" it up. But I know it's awful on hair. The hair can wait until the evening shower, and possibly the body, but I wouldsay to at the very least rinse, head to toe, and if you have the time, take a handful of body wash and maybe let it suds up, run it over- to get the main stays off. But if the kids don't wash up after, don't let them go to bed without a good shower and wash down.
Hope that helps! Have loads of fun swimming!