It’s easy to say “I’d never let my kids do X!” when you aren’t a parent. But no one does parenting in a vacuum. Or at least, they shouldn’t. If you do, you’re probably not a great parent.
Why do they want to see it?
Think back to when you were a child. Why did you want to see a cartoon you’d probably find lame/stupid/etc. now?
Because the corporate forces marketed it heavily during my Saturday morning cartoons.
I still don’t understand the point of your question.
It was just a question, there was no point.
Ok fine, I assumed you were trying to make a point because otherwise the answer should be obvious. They’re little girls who love My Little Pony. That’s why they wanted to see the My Little Pony movie.