Well.... Since I doubt we're going to be able to meet at a convenient time when both of us are online, I have series of questions I'll just leave here for the brainstorming effort:

[indent][i]You mentioned two worlds. Is one of them current=day Earth, or is it simply a place with is Earth-like? Is the other world earth-like or does its structure and style adhere to something more fantastical, like the mythological imagery of Elysium, Hell, the Feywilds, and Asgard? 

As far as the balancing mechanism between these two worlds are concerned, what ties them together?
Reincarnation cycle perhaps? Those who die in one reincarnate to the other, so their is only ever a finite amount of souls. One world being well-populated and the other a near-apocalyptic wasteland? Are they tied by magic? Is there predetermined amount of magical power available, which is split between these worlds? 
To take this idea further, maybe while the original world enjoys a significant technological renaissance since the decline of magic in more ancient times, the remaining magic retreats to the other world where the scales are tipped in magic's favor. Perhaps there too they experience a potent evolution of fantastic magical advancements.
Maybe this scale of shared magic is occasionally shaken. Magic retreats and returns in waves, like a pendulum, marking the beginning and end of long eras in each world.

When the primary character traverse into this other world, do they maintain their form? Are their bodies "translated" into something more appropriate to the setting? Would such a translation confer to our(?) characters the ability to overcome language and cultural barriers? Is this the universe's way of maintaining balance?
Put another way, if our character left to fend for themselves in a foreign land with no knowledge of this other world, no inkling of the language and norms, is this great obstacle something they are to overcome? Is there a a middle-ground which can be achieved, where only partial changes are made when traveling to the other fantasy world?

How does the protagonists meeting their end goals affect everyone else? Who stands to gain from it? And, who might expect great losses from their accomplishment? Is there a clear distinction of moral agendas such as "good" and "evil", or are their simply multiple actors trying to carve out their own space in the story? 

You mentioned an emphasis on cuteness, adventure, and sense of wonder. How did you envision those aspects taking shape within this story? 

I'd assume these protagonists much be cosmically important to have been swept up into such a grand plot. Is their a sense of Fate working behind the scenes? Or, instead of the protagonists, would anyone have been fine? Why and how important are these characters in the cosmic scale? Are they important at all? Is it simply their ideals that propel them forward? Love? Revenge? Is this kind of motivation something you wish to have unfold as the story progresses?[/i][/indent]

(I really could go on, but I've run out of time. >.<' TTYL ;3)