Usage of 'had been' or 'were'

I was doing an exercise. I completed the sentence as following.

If you were my child, I would have demanded that such an irresponsible teacher be fired.

But the answer given in the book is following.

If you had been my child, I would have demanded that such an irresponsible teacher be fired.

I am not sure if my answer is wrong. The latter sounds better and I can see the relative merit of it.

Your answer was wrong. Would have demanded in the main clause requires had + past participle in the 'if' clause. The construction is sometimes known to foreign learners as the third conditional.

I think the book is wrong. Superficially, #1 seems to "mix tenses", but I'm not going to claim that 1710 written instances of "if it were me I would have..." in Google Books are all "ungrammatical".

You can explicitly place your "subjunctive postulate" in the past (you were my child, it was me) to agree with a following clause saying what might have happened in that case, but I don't see that any such agreement is necessary. I personally have no problem with any of...

"If it were my house, I'd have redecorated last year"

"If it had been my house, I'd have redecorated last year" (where you might actually own it now)

"If it were my house, I'd sell it next year"

"If it had been my house since 1970, I'd sell it next year"

If you want to get top marks in an exam, #2 is the obvious choice. But that doesn't mean native speakers don't habitually (and validly, imho) combine tenses in such constructions.

EDIT: I also think the choice of example in OP's book is potentially confusing, because the "contrafactual postulate" (that you are/were my child) is "temporally independent" (if it wasn't true in the past, it can't be true now either). People wouldn't normally say, for example,...

If there had been a God, he wouldn't have drowned the last unicorns in the Flood.

...because that admits of the awkward possibility that there wasn't a God then, but there is now.