Yes a child with fifth disease or slapped cheeks can go to school.
That is once the child has the rash from the fifth disease they can return to school because they are no longer contagious with the fifth disease.
When the rash appears from fifth disease the child can no longer spread the fifth disease to anyone else so they can safely return to school.
The fifth disease can only be spread during the week before the rash begins.
After the rash appears it's safe for the child to return to school, daycare etc.