The police put out a statement about this, saying social media was misrepresenting it. I can't remember exactly what it said, but it seemed reasonable sensible.
The main fault was the ex clearly. I doubt extremely that he wasn't totally aware of the situation. I can't remember whether the police report said he'd been cautioned for wasting police time or just spoken to, but they were pretty clear that they felt it was on him.
But mum could have avoided it by saying the true situation. They won't have walked up and arrested her without and chance for her to say "the only iPads here are the kids and they're confiscated due to xyz". I don't believe it didn't occur to her at any point that if two iPads were showing on the app as inside, which they told her, that they were her kids. She denied she had iPads, I suspect more than once.
For what end she denied it I cannot think of any sane reason.
I suppose she could have been hoping that it would come back on her ex, in the way it has, but it's a risky strategy, because you can't predict SM.