I was worried about this too but it's been a lot less trouble than I thought.
Nuclear family films were actually good for us because it reinforced our family setting and let them see families that looked like ours - obviously that's only going to be good if that's how your family looks, but it meant things like Peppa Pig were a winner with me.
I was more bothered by the films where mum was absent, of which there are many, particularly if the point of the movie was to seek out mum, because I was worried they'd be relating to it wrt to BM. Once I realised they were relating to it wrt me (or not relating to it at all) I chilled about that a bit more.
We avoided anything obviously about adoption/fostering for ages, but it sneaks in to everything, (The Rescuers, really? Bedknobs snd Broomsticks? Who knew?) so I gave up on that and just make sure I keep half an ear listening for anything wildly inappropriate. (So watching Annie, I made sure LO knew that was a fictionalised system in another country and not like what had happened to her.)
Things we still avoid are things designed to tug at heart strings. (The Good Dinosaur, I'm looking at you, and I'll not be seeking ET out anytime soon). That's just because we have an abundance of crazy emotions anyway, they don't need to be artificial provoked!
And finally, there's the Adoption at the Movies review site. No idea who it's by, but it's great.
www.adoptionlcsw.com/?m=1