What Causes Bumps On The Abdomen And Face?

My twin boys have been vaccinated for chicken pox and I just got a call from their Grandmother who is keeping them for the week, she has described what appears to be chicken pox. Do I need to get them to a doctor or it is ok to treat the symptoms and let them continue their stay? Also, can they go swimming at a pool. They say they don't itch but they complained of stomach aches on Friday and the bumps have started today on their bellys and faces.

Thanks