The "protagonists," the goo-balls, die a lot. You have to sacrifice them, sometimes, and I'm really sad to watch my structure die and scream and squelch. However, if you don't repeatedly fail, you can bring them back to life by popping one of the little white bugs that are created with every move. There's some weird-looking things, too, and the occasional dark comment by the Sign Painter, but not too dark. Very cartoony, but still, kinda dark. Not very, though. Cartoon violence, as it most likely says on the ESRB rating. Some levels are very challenging; children may need advice if they are confused sometimes, though not often, as the Sign Painter usually has a few helpful hints for anyone observant enough to see the relatively-obvious signs.
P. S. Very addictive... All of the painfully difficult levels can be skipped, however, since there's three level-skips in every world.