Don't be a dick
Your fun isn't wrong
I think Stuffed Fables is a bit easier from the Rules and Storywise, you don't fight as much. I think Stuffed Fables is the slightly better game, as Mice and Mystics sometimes gets repetitive.
Both games are absolutely fantastic on the Theme department and can be very rewarding as a family experience. Mechanics wise, they both have their problems (a German reviewer said recently it's the favorite game of a friends of his because of the time he had with his son, even if the game isn't as good as other games mechanics wise). But for the mechanics department, you have My little Scythe there, so:
If it's not for their birthday and/or has to be a surprise, ask your kids which theme they prefer! That's the strong suit of both of these games anyways.
I did ask them, but it just comes down to aesthetics and theme for them (Stuffed Fables won out). But I have been bitten before buying untried games that looked and sounded great...
Thanks for your thoughts though. They were exactly what I needed. They want Stuffed Fables too.