After doing a lot of research, we also decided to put our 3 1/2 year old son with asthma on Flo Vent. We went to a pediatric pulmonologist and she recommended we do this. The damage done to his lungs if we had not done anything would have been much greater than any side effects from the steroid.
We have not noticed any side effects. One of the side effects we are worried about for the future is the steroid effect on growth. Our son is pretty small to begin with. However, the effect is overall small- studies show that it's only about 1 cm, meaning that children on the drug tend to be 1 cm shorter than they would have been if they hadn't taken it.
So,we are happy with the drug and our son has not had any asthma attacks since he's been on it.