your little one needs a us passport.  takes about a month to apply.  need to submit a original birth certificate with it.  they will return it with the new passport.  both of you need to take a little one to apply for the passport.  mainly at the participating post offices around the country or the court house.  just log on to www.state.gov and search for passport.   you can apply for baby's visa at the kathmandu airport.  there is no fee for the baby however.  make sure to have baby's extra pictures for the visa.  they have been giving two months visitor visa.  visit nepal embassy websute in washington dc for detail.  as for baby travelling,  baby may be too big to have a basinet on the plane.  i forgot the weight limit.  check with the travel agency or airline website.  believe me that would come handy.  you do have to pay less than $500 for the baby,  it is mostly taxes.  fare is like $100 rest is taxes.  also make sure to buy a cheap stroller and can carry all the way to the gate.  so you will have it whenever you have a transit.   make sure you ask for the stroller before leaving the plane. 

one more thing, when you get baby's us passport.  mom or dad needs to write his/her name.  sign it and make sure to write down either mom or dad.  more on this at the site.  or ask at the time you apply.  you can download the passport form from the website.

hope this helps.   i have been through this twice with two kids.  let me know if you need further info.