I downloaded FirstFable after playing Hero Kids with my 6 and 8 year-olds to check out some of the other kids' games.
While the art in FirstFable is really nice, the game isn't as good as Hero Kids for my kids. FirstFable requires a long character creation stage before you can play, even when playing with one of the four characters that come with the game. By contrast, Hero Kids has characters ready to play (and you can make your own if you want), and it has 10 diverse heroes, including boys and girls.
Once we got playing FirstFable, the kids found the game complicated and somewhat abstract. My kids had trouble with their Shines and Stars, and couldn't grasp how much damage to use in combat. Having come from Hero Kids, which has simple combat and ability tests, this was all too much for kids their age. And the character sheets are very text heavy, which is also a huge barrier for the younger kids.
Ultimately, I think that this game is more appropriate for older kids, say from 10-12. But by then I expect my kids to have graduated to full RPGs instead.