Just checked with minor with her oci ,old passport and new passport .
They did not even ask for oci card .Checked in on U visa and new passport in Emirates at stansted

My wife travelled yesterday with minor from stansted with minor .only thing they asked was for lifelong visa on old passport .
The family may be travelling without old passport which has lifelong visa

Emirates

Update
My wife travelled yesterday with my son who has new passport .She travelled with old passport and new passport and oci card .She was told that he has lifelong visa on his passport which is valid so no problems .

letter from immigration delhi BOI SUPPORT CENTRE <support-boi@mha.gov.in> To: Nov 30 at 6:50 AM Dear Sir/ Madam, Your son may travel to India on his OCI card and valid Passport but it is suggested to carry old passport on which OCI card was issued to avoid undue/unforeseen delay/trouble. You may do ...