I posted a review on the game's site here on GOG, but let me elaborate on some points.
Kid friendlyness: I'm torn in this regard. The art style is quite beautiful and the overall design is surely aimed at kids. Most of the puzzles are also quite easy, mostly because you can only click some spots at any given time. So, most of the puzzles can be solved by simply trying out your options. There is, however, a colour puzzle that could be quite confusing for kids. You certainly need some knowledge in how colours are mixed. This puzzles get repeated throughout the game. That said, there are some puzzles involving machines without giving you many clues as to what they do. I guess, kids could get frustrated with that.
[much goodness snipped]
As much as I wish I didn't, I agree with Cardian on all points (with the exception of the final color puzzle, which I felt was completely void of any sense of direction and, thus, more difficult). I just want to also add that the game ends with a cliffhanger that (**vague spoiler alert**)
places both kids in a potentially peril situation. This may actually be disturbing, particularly for younger players, and especially if they've formed any connection with the characters.