What I did once in that situation was to detect if the Parent had at least two future children tasks.
I set up a saved table to table import to copy the parent into the child task table and populate the task due date field as the parent would know the frequency of the task and the most future task created so far.
Then I set up an automation to import the parents who did not have at least two next future dated into a child table to create the next Child Tasks for all parents. I ran the imports twice each day in the same automation.
So that way each night after midnight, I would know that each parent had at least 2 future tasks.
