My sister babysits for a few children does she have the right to call doc?

She is babysitting a child about 6 months old, he is very congested and seems just miserable, he has a runny nose and you can hear the congestion in his lungs. As of the past few days he has been without fever. The mother refuses to take the baby to the doctor, and claims he has allergies. She has stated other day care facilities have also state they thought the baby was sick and this only upset her. Currently, the other children my sister watches have come down with the same symptoms. Does my sister have the right to call the childs doctor to ess the symptoms being as she is in control of the childs well being during the times she has him. ??