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The child must have a passport (or refugee travel document) to travel, and in order to enter the US must have a US visa. If the child does not have a passport, you must apply for and secure one for the child before you travel.
After the child has a passport, then you apply for a US visa for the child. The child can travel to the US if a US visa is issued in the child's name. The visa application process begins online.
Note that this answer relates only to passport and visa issues. It does not address covid-related requirements or documents.