Disney's "Phineas and Ferb" was co-created by one of the directors from "Family Guy". That's why their humor is so similar.
Family Guy's Dan Povenmire was hired by Disney to make a cartoon show, and they were apparently impressed by his work on Family Guy (even though the humor is too raunchy for the Disney Channel.)
According to Povenmire: My work on Family Guy didn't scare Disney. In fact, it had a huge impact on them, wanting to see whatever I did, because Adam Bonnet [Disney Channel's senior VP of original series] is a big fan...
What we tried to do with Phineas and Ferb was put some of that primetime animation timing and sensibility without any of the raunch. We do a lot of stuff where we try to get a gag with a pause or a blank stare -- something really big happens and the other person just stares at him.