Ok so I've been a long time GM for my group and have, typically, been running 40k things (dark heresy, rogue trader, etc). We've played things like DnD and World of Darkness (norm/vamp/wolf/mage/promethian, etc) and I like to put a darker spin on most stories. Grimm interested me in that I like the semi-dark setting spattered with a bit of insane whimsy. This said I am a bit concerned as to how my players will take it (I've only read so far up to magical dueling, have yet to really get into the stuff later in the book) as the game does seem extremely kid oriented. Not just in theme given, but in stats.
Is it possible to run a dark and not "to" whimsical game of this, ie what are your experiences with players? Do older players (we're looking at late twenties to early thirties here in my case) adapt to this well in your experience? If so do you have tips on things you did to acclimate players not used to playing kids into the game?

I am going to be new to Grimm and running the game…However I have run D&D 3.5 for a few years now came across Grimm and thought I would give it a try.