If you are going Nepal via India with your Kid with US Passport, you need VISA for India which will be provided in Arrival to INDIA. Better to talk to the Indian Embassy before you proceed. You can goolge INDIAN EMBASSY and get tel number. If you are in USA, you can contact:

2107 Massachusetts Avenue,  N.W., Washington D.C.
USA - 20008
Phone: (202) 939-7000
Fax: (202) 265-4351