It is usually fairly mild in children. Most of us will have encountered the virus- usually a cocksackie virus- at some point in our lives. It causes, as its name suggests, spots on the hands, feet and around and inside the mouth. They are flattish and crust over after a few days. However, it can be quite nasty for adults: my daughter was quite poorly with it. I cared for two grandchildren with it, and spent time with my poorly daughter, and I haven’t caught it. But then, I used to be a teacher in an infant school, so I think I have a good resistance to most things.
The NHS website has information on it.