You mentioned that the children were born in South Africa.  But if the American father satisfied the US residency requirements, his children would acquire American citizenship at birth.  Did they apply for an ITIN because the residency requirements were not meet?

Were these SSNs issued only in 2020?  If so, leave the 2019 return as is.  Just make a note on your file to use these on the 2020 return.

If these were issued in 2019 and you must correct them, the best way to do that is to call the IRS, which is resuming operation in phases.  However, especially if no 1099/1098s were issued for 2019 under those SSNs, there's really no urgency to get that updated.