When you mention 'visa' I'm presuming you are referring to the "U" Visa in his passport corresponding to his OCI status.
Since 2015, India has ceased issuing these visas, and they are no longer required when entering the country - you only need to present your OCI card.
You will find this information stated on many official websites, such as the Bureau of Immigration website (towards the bottom as Note 1) :
Government of India has decided to dispense with the "U" Visa sticker
on the foreign passport of OCI card holders with immediate effect.
Accordingly, Immigration authorities shall not insist on production of
foreign passport containing the "U" Visa sticker in the case of OCI
card holders while they enter/exit India. OCI card holders shall now
be given Immigration clearance on the strength of their valid forign
passport and OCI Registration Certificate (OCI booklet, popularly
known as OCI card).
In addition to this change, India does generally accept visas that are contained in prior passports, and the 'damage' done by removing the machine-readable strip on the bio page does not invalidate that.
HOWEVER if your Son is below 21 years of age, then he is required to obtain a new OCI card whenever he obtains a new passport. This is not related to the visa, but to the OCI card itself. The same is also true when passing 50 years of age.
Further information on this can be found on the CKGS website (CKGS is the company responsible for Indian visas/OCI/etc in the US, so it a legitimate company/website)
