My two little 3 year old boys have fleas for the first time. I am horrified and I am not sure what to do.

I took them ot the Vet and she said they have fleas and reccomended Vectra 3D. They are only 8 and 9 lbs and I am afraid this is going to be to strong. Any advice on a less harsh but effective treatment? I gave them both a bath with flea shampoo and it seemed to help and tomorrow I am taking them to get another flea bath and their hair cut short to help with the flea issue but I need to get them on some sort of medicine. Any advice or direction is greatly appreciated.

btw...we recentley moved and the new vet we went to was totally weird so I didnt feel comfortable asking qs..