This is the bug of the week in Austin, TX....and probably many other places across the country. Typically, we see this virus (official name: Coxsackie virus) every spring and summer. It's not serious, but it is contagious. It spreads through infected saliva—so little kids who put toys in their mouths are notorious for spreading it through daycare. Young kids will have a fever and may be no other obvious symptoms to mom and dad. Except, they are less interested in drinking because they have sores in the back of their mouths. If you are lucky, there is a rash on the hands and feet (like the one in the picture) to confirm the diagnosis.
I personally think it should be called hand,foot, mouth, and anus--because sometimes the rash ends up there too.
Photo courtesy of Jason Reichenberg, MD, dermatologist.