If you have preschoolers, especially, but also perhaps elementary-aged kids, they will probably love Poisson Rouge as much as we do.
The makers of Poisson Rouge didn't post instructions on the site, as they'd prefer that children freely do whatever they'd like to do on Poisson Rouge, but with more than a little reluctance, they wrote up a User Guide for Teachers & Parents, which is well worth a read not only for the lesson tips, but also for their insight into how children learn.
Here are a couple of reviews posted on Poisson Rouge:
"I have a little girl just about to turn three and she loves it. It has done wonders for her mouse skills, unlike any other websites we have found she can use it completely independently and she is still finding new things to do on it."
I dare you to try not to get addicted to Poisson Rouge yourself!