A well made, gentle movie suitable for a range of ages.
Our family loved this movie. The word that comes to mind is "gentle." Scenes that could otherwise be suspenseful for sensitive children (gathering storm clouds, children by themselves in a barn at night, etc) are kept calm by a gentle piano music score that continues throughout. It's lovely and well done. (A little reminiscent of Studio Ghibli scores.) The animation is quite beautiful, as well - simple, but thoughtful and visually appealing. There is a scene of real life danger involving the children and the tide coming into a cave, but the way the older siblings help the younger ones makes the scene bearable (again, to sensitive children; probably most kids wouldn't find it more than "adventurous" in the first place. It might be advisable to watch along with sensitive young ones just in case). There is also a human skeleton the children partially unbury in the cave, but again, the way the characters and music remain calm and discuss it rationally help the scene unfold without the scariness it could have. Again, you know what may be problematic for your own child. Mine are pretty sensitive but did okay with this.
There was a mention somewhere that said the movie had no ethnic diversity. That's almost true, but there was one recurring character who was clearly Native American, and was portrayed respectfully and in a positive light. (My kids are a tiny bit Native American and the character reminded me of their grandfather, in the best ways.)
Positive aspects: the siblings do not fight. The older ones really care for the younger ones and model responsible behavior...it's refreshing. The children are also respectful toward the adults and other characters. It's maybe worth noting that the story is set in an earlier time when kids could be given more freedom/responsibility (a good point for family discussion). The children are quite capable of independence from the adult characters, but they don't abuse the privilege.
The only thing I could see as a "negative" (but wasn't, for my family) is that if kids are used to typical entertainment fare they might find the pacing slow...I think it's done intentionally, though, so for a family looking for a calm, enjoyable family movie with an uncomplicated (but still intriguing enough for kids!) plot, it's really ideal. Our kids' ages range from 5-10 and they all LOVE both Boxcar Children movies because the main characters cover a range of ages, so each child can relate to at least one character. I personally just like watching a movie with my kids that has beautiful (animated) scenery, kid characters that aren't bratty and actually love each other, and adult characters who act like (mature) adults. It's refreshing.
We own both movies, and if they make more of them we'll buy those, too.