I've only skim-read, but I saw this thread earlier so I wrote out the question for DD (just finished Y1, she's still 5 though) and asked if she knew the answer. She said "yes, 16” and carried on eating her fish fingers. She told me "just is" when I asked why, so I asked her to explain to her 3yo DB.
She said "7 is what take away 9, which is the same as 7 and 9 make what?" and then she helpfully wrote out a number line for DS and showed him how counting forward nine from seven would give him the right answer too.
She seemed very confident so I can only assumed that they have looked at both methods (I'd not heard of the term 'fact families' before, but certainly the way DD talks about numbers, eg today "8x3 is 24, and so a third of 24 smarties is eight", makes it sound as though that's exactly what they've been taught).
I don't know that this adds much to the thread, but I was intrigued to find out how a Y1 child would approach the question as I wouldn't have a clue how I'd be supposed to explain it these days. Fortunately it seems I don't have to, it's been done already!
The Dragon Box app sounds interesting. Thanks to the PPs who mentioned it.