Fushigi no Umi no Nadia, Fractale Recommendations
These two series may be seem lighthearted and family-friendly, but they both have something to offer for audiences of all ages, and have similar tones of good clean fun with a more serious plot lurking in the background.
Also: both are about a group of children and young teens who are swept up in some sort of adventure. Both take place in a world with elements of both our own world's past and the technology of the future. And the trio of villains in Fractale was almost certainly influenced by a similar trio in Nadia.