I think you can travel with the infant. But, the baby needs a american passport, which you can apply and get from the nearest post office. Also, baby might need a ticket (round trip should not cost more than $200, I guess). I suggest you to take baby's immunization record to provide other shots in Nepal. They will provide VISA for your baby at KTM Airport. In addition, I have heard that it is safe to carry one to two unopened can of baby's formula while you return in case the baby needs in aeroplane, because they don't provide you to carry any open food from Nepal. Most Airlines will provide baby's bassinet in the plane, just you need to ask for the front seat for you and tell them that you have infant.