Thanks Hilary - it's good to (at least) get confirmation that it's not possible.
Regarding saving the data - I'm going to be saving this as a library file (along with a couple of concat'd fields), so I'm okay with the data not being directly available outside of the completed form.
My main goal is to have the answer to a Parent question result in the appearance of Child questions. So, if Question 1 is "Yes", then show 1a, 1b, etc.; if Question 1 is "No", then hide 1a, 1b, etc. Therefore, each row with have a "Yes" checkbox: if yes, show children; if no, hide children. I've got this working fine with questions hard-written into the form and associated child sections; but I was hoping to make a 'blank' form that could be fully populated via lists (that way, non InfoPath folks can create their own cascading forms).
I initially had a single, flat list that included Parent and Child questions (see my new attachment). But what I couldn't figure out was how to hide the child rows. In text, the rule is: if the field Yes in the Parent row equals "yes"; and the field Child =equals the field Question Number, then show; otherwise, hide. I thought briefly about the preceding-sibling formula, but I don't really know the correct syntax of that one (I've used it, but only when copy/pasting from an example!), and I didn't know if could accommodate multiple Child questions (e.g., 1a has 1 as the immediate predecessor; but 1b has 1a as the predecessor. Maybe something like: show the row if the preceding row has Question Number = Child or Child = Child).
Anyway - I really appreciate you thinking about this. I've attached an updated example; if you have any thoughts (or a good link) to preceding-sibling syntax, that would be awesome!!