This is a fun movie that offers a good storyline and I definitely recommend it for anyone looking for a kid's action movie. We also really enjoyed Sea Beast on Netflix for comparison.
Since none of the negative reviews actually discuss the story I'll say this: As we watched this with my two year old, I made the comment that if more movies normalize the diversity represented here, my son will grow up in a world where people don't even think twice about representation, it will just be expected and they will question spaces without diversity. Wouldn't that be great! An entire culture of kids who don't hold to their parents' generation's prejudices.
There is nothing inappropriate in this film. The romantic relationships are clearly not the focus of the film. If you don't have a problem with your child watching kids' movies where romance is the base of the story, like Little Mermaid (a 16 year-old girl literally changing her body to meet a boy - wearing a bikini during the movie completely aside) and Aladdin (a boy lying about who he is to impress a girl). You need to take a hard look at what you find inappropriate about this film.
This is the next generation's Fern Gully, the Lorax, and Happy Feet. Taking care of the environment shouldn't be a divisive lesson.