This is a good movie but not what I expected as the follow up to the original Cars. I watched both with my 4 year old (first time seeing them for both of us). My daughter loved Cars and I did too. Really entertaining movie with fun and funny characters with some positive messages in it. The "darkest" character being Chic Hicks who is simply a self centered schmuck. I had no qualms about letting her watch this.
Although Cars 2 is also rated "G" it is in stark contrast to it's predecessor. It has a dark feel to it and clearly inspired by "James Bond" movies. It includes a lot of gun violence and the bad guys are instructed to "kill him! And some characters are even killed off. There is also some mild name calling. Don't get me wrong, as an adult, I thought it was entertaining and I've even watched it more than once. Just know going in that it is definitely more "mature" than the first. Had I know beforehand, I likely would have put this one on hold for a later day. Hope this helps.