If I understand correctly you have a child list that connects to the parent list using a lookup field that shows the value from a field in the parent named RefID.
In that case you can use this setup in the vLookup configuration in your parent form to list all connected child items (luRefID is the internal name of the lookup field in your child list):
luRefID eq '[[item:id]]'
This config will match the lookup by ID which is more reliable, but you can also use this format to match by the display value:
luRefID/Title eq '[[fieldValue:RefID]]'
Let me know if you have any questions.