Yes since fifth disease is contagious that means that an adult or anyone else near the child who has fifth disease can get the fifth disease from the child.
As long as the child is contagious with the fifth disease and the adult or parents are around the child they too can get fifth disease.
Not all adults who are around children will get fifth disease from the child who has it but it is possible.
When an adult gets fifth disease they usually have symptoms such as a severe flu like illness but rarely does an adult develop the rash with fifth disease like a child does.