In the below link, nowhere there is a mention of where the US citizen child should be, whether in the US or outside while one of the parent travel to the US under the exemption. So I believe you should be able to travel.
Call the specific embassy to double check.
The Proclamation does not apply to:
- Any non-U.S. citizen who is the parent or legal guardian of a U.S. citizen or LPR, provided that the U.S. citizen or LPR child is unmarried and under the age of 21,
Qualifying family members do not need a National Interest Exception or any preapproval from the Embassy or Consulates. travelers should bring proof of relationship when initiating travel to the United States.