Unmarried son/daughter of a US Permanent Resident over the age of 21 with Kids

[Bella T]

An unmarried son/daughter of a permanent resident has kids, and the I-130 petition has been approved by the USCIS and is now being processed at the National Visa Center. What exactly is the process to bring the beneficiary's kids to the US? Wait until the beneficiary is called into the US Embassy for Visa disbursement? Or is there some other petition that must be completed beforehand? One of the kids was born before the I-130 was filed and the other after it was approved and sent to the National Visa Center. Thank you very much for your input.