RSV is respiratory syncytial virus. It is the most common cause of bronchiolitis and pneumonia among infants and children under 1 year of age. Most children hospitalized for RSV infection are under 6 months of age. RSV is spread from respiratory secretions through close contact with infected persons or contact with contaminated surfaces or objects. The RSV infection is passed much like the common cold and/or flu - when germs come in contact with the mucous membranes, the eyes, or are spread with droplets like from a sneeze.
It can take up to 2 weeks for children to recover from RSV infection, but they can have lasting implications - causing more colds, flu, ear infections, etc.
You can look up all this information on the CDC website.
Basically, kids pass mucky germs around to each other. They are like little petri dishes!
Good luck to your God daughter! I hope she feels better soon.