Hi @Francis_Simon,
You can recall a variable by typing ${var-name}.
e.g. if the variable you want to recall is called childname, than you would write ${childname}
The syntax is a bit different if you refer to a variable inside a repeat group.
In this case the app would get "confused", unless you specify which iteration it should consider. The command to use is:
indexed-repeat(${var-name}, ${group-name}, position)
For more info on the ODK syntax, please see: https://docs.opendatakit.org/form-repeats/?highlight=indexed%20repeat#referencing-answers-from-repeated-questions
I hope this helps!
Best,
Andrea