Hey,
My suggestion is to go with ListView, you can easily match styling to be same as DataGrid.
And to solve your problem you can display list and add OnClick function to item from list where you can just create simple microflow where you can just fill association between your selected "child-object" and "parent-object". For showing which one is selected you can just add Dynamic class on container that you look something like this if $currentObject/parent-object_child-object != empty then 'selected' else empty
Best regards, Slavko