Yes it certainly is possible for a child or even an adult to get roseola twice but it's rare that a child or adult gets infected with roseola twice.
Most times a child or adult only gets the virus causing roseola once and then they build up antibodies and immunity to the roseola virus.
Also most children who get the roseola virus get it before age 5 and don't get it again.
Once a child gets roseola and develops the roseola rash the rash itself usually goes away on it's own within 5 days after the fever is gone.
The fever that a child or baby has with roseola lasts about 5 days and then the roseola rash follows and lasts up to 5 days.
You should keep your child home from daycare, preschool etc until the child has no fever with the roseola.
Your child can go to daycare with the roseola rash as long as the child with the roseola rash has no fever.
If the child with the roseola rash has a fever then you should not send them to daycare because they could infect the other kids at daycare.
The virus that causes the roseola rash has an incubation period from time of exposure to the virus to symptom development from about five to 14 days.
So if your child has gotten has gotten infected with the virus causing the roseola and roseola rash then keep them home for at least 14 days from daycare.
Then after 14 days you can return your child to daycare as long as they have no fever.