It might be fun to twist magic a wee bit...
Say, make it kinda like the 'different psionics' option...all magical creatures have a specific template you can apply to them, and non-magic folk (humans, mostly) find it hard to resist or overcome their powers....
Of course, the Wizard class would probably be restricted 'by training only.' Some other races may be fey (Pixies, Dryads, Satyrs, even the smaller elementals or younger dragons).
I guess it depends on how much you want to play in the fairy tale world. If you're full-on fantastical, you don't need Humans at all, and you just describe the roaming adventurers, thwarting the designs of wicked queens and kings in the name of goodness, using trickery and illusion as the most powerful weapons. They travel only at night (because daylight is deadly to most of the Faerie), and may even do good tasks for humans, perhaps at the behest of the elf king that lives in the shaded glenn, or perhaps at the behest of higher powers of the universe. Mystery is an important element, as is the ubiquitous nature of minor magical flourishes. Think of a 'lunar' theme...the moon changes constantly, altering the light of night and the visibility of the world at large. Perhaps it even opposes the 'solar' world, the world of the humans (which is why kitties and wolves are somewhat fey -- they're noctournal). The world you interact with is one of continuous riddle and mischief, some of it harmless, some of it deadly. And some of it perpetuated by those fey who utterly lothe everything beautiful and pure.
If you want humans in the mix, but don't mind a few PC's being fey, it's a lot like above, with perhaps more emphasis on the conflict between the two worlds. The humans may be touched by the fey, or recruited by them, or they may seek out the fey and join their crusade. Either way, the two live in different worlds, with the magical being mostly inexplicable to the mundanes, but a few mundanes can figure it out.
If you want to go pure human/mundane, your world should be filled with nighttime mischief, illusion, and trickery. Everything should be an allegory, and the only way to solve the adventure is to figure out the riddle. Things like levels and CR's become less key, since fighting isn't the way out of most situations. You can pit a party of four commoner children against a massive red great wyrm, and have them come out better for it because of their magical amulet of mother's love, or their pure hearts for helping the out-of-sorts goblins earlier.
It's not a matter of the tales being for children, it's a matter of the children's mindset -- the world is full of potential, wonder, and unexplored corners with secrets just waiting. Some are good, but some want to get you and eat you up. Even the adults must exist with this mentality (though they could have their own worlds pretty well 'figured out,' and 'don't want no truck with the unnatural'). The unknown is a powerful force, for both good and ill, and no matter how much you discover, there's always more waiting.