Let me ask you this; what's the difference between a kid's movie and a family movie? On the surface, both of those terms might seem interchangeable. A movie that's for kids is theoretically appropriate enough for a whole family to watch, but there's a lot more to it than that, at least in my opinion. Sure, a family could get together and watch The Angry Birds Movie, but unless your mom or dad loves watching green pigs shake their butts at a camera for 90 minutes, it's not going to be enjoyed by everyone equally. In my eyes, a good family movie is one that every member of a family could enjoy together but for completely different reasons.
Case in point, I would argue that a lot of anime movies would qualify as great family films. Movies like Kiki's Delivery Service, Spirited Away, Ponyo,and Mary & the Witch's Flower are all fantastic movies that can entertain kids with their pretty visuals and fun characters, while adults can enjoy them for all of that and the themes those movies tackle. There's no inappropriate language if you're a stickler about that and the messages are always positive and healthy for a developing child.
I feel fairly certain that I can call Miraia great film for little kids that parents can watch with them for a family movie night.