What are you planning on changing?
Surname or Given name?
Either way the process is a pain in da tuss~
You can change your kids name here in the US, but the Indian Consulate does not recognize the orders issued by the US Courts. You will have to change your kids Name in India (to be precise in the State and City he/she was born). Once you file the name change it will be published in the Gazzette. After which you need to take that publication and get a magistrate order. Once this is done, you will have to insert an Ad in a national newspaper in India, and in the US. Wait for a month after the publication, fill out a new passport application, attach the news papers (not the cuttings of the Ad, but the complete newspaper)which published the Ad, the Magistrates order, and your kid will be issued a new passport.
Also I am not sure as to Which City/State your kid was born. If your kid was born in Madras, you or your spouse will have to be present for the whole process (till the Magistrate signs the order), since no one else can do it on your behalf.
Good Luck!!