"Family Guy" is in the business of satire, mocking everyone from the right, the left, politics and non-politics. Sarah Palin's son Trig, who has Down Syndrome, is the target of a recent episode.
In the episode, the main character, Chris, dates a mentally disabled girl. While never mentioning Palin by name, the girl drew a clear comparison to her son, Trig, when she told Chris, "My dad's an accountant, and my mom's the former governor of Alaska."(see the Huffington Post article here)
Palin posted on her Facebook page that it "felt like a kick in the gut" and Bristol Palin said the "All they (creators) proved is that they are heartless jerks."
Attacking Sarah Palin is obviously fair game, which South Park and others have done very well. Attacking the infant's genetic anomaly - crass, tasteless and below the belt, even for Family Guy.