To get it stamped, the passport should have a validity of at least 6 month, at the time of submission at the consulate.
If it does, and you get stamped, upon return the immigration officer will have the I-94 stamped only until passport expiry date in 2018, even though the petition is valid until 2019. Technically, you cannot stay outside India on a expired passport, unless you renew it before it expires. In case, the immigration officer stamps the I-94 to 2018 validity, you may have to re-apply for extension of status to USCIS from I-94 expiry date to I-797 expiry date and has to be approved by USCIS.
By all means, please renew your son's passport now, to prevent any unwanted issues in future. You can have it with you, here in USA in 2 weeks, so you still have time to apply before Feb 2018. You may also do it in India, if you wish. But it is good to have a new passport in hand when you return to USA to prevent the I-94 validity issues.