All children under the age of 18 with LPR status automatically becomes a citizen when the father becomes a citizen, also, children under the age of 18 who migrate to the US with a US parent will automatically become US citizens. So go to india and bring your child, he will get US citizenship! provided he is under 18 when you do so. unfortunately, you wife needs to apply for PR all over again, which I have heard can be a pain when you give up your "green card" voluntarily.
"In general, children who are younger than 18 years of age and have at least one parent who is a U.S. citizen whether by birth or naturalization will benefit from this new law. Under the CCA, qualifying children who immigrate to the United States with a U.S. citizen parent automatically acquire U.S. citizenship upon entry; children who live abroad acquire citizenship on approval of an application and the taking of the oath of allegiance." - USCIS
http://uscis.gov/graphics/services/natz/CCA_Update.htm