You need to apply for OCI Miscellaneous Services and select option to transfer sticker to new passport. Your child falls under point one below.
https://ociservices.gov.in/capchaActionMisc
These Misc services can be availed for re-issuance of OCI Card as well as updating the information time to time as mentioned in the MHA notification dated 16th April, 2021. The re-issuance of new OCI card will be applicable for following categories:
1. In case of issuance of new passport (once a new passport is issued after completing 20 years of age.)
2. In case of change of personal particulars viz. name, father's name, nationality etc.
3. In case of loss/damage of OCI registration certificate.