They all have wacky heads, but its because of their hair. Lisa, Bart, and Maggie have spikey-looking hair that appears really short. Yet Bart and Lisa's hair have been shown longer and more realistic. Like when they go to church or something, Bart parts his hair, and several times Lisa has had hairdos done which implies her hair is longer and straighter than the triangles it looks like.
I realize its a cartoon, but it's like they grow and lose hair for the sake of that episode's plot device. It would make more sense if they had a clear hairline, but they don't. Its like their hair is an extension of their forehead.
Ned Flanders, Barney Gumble, and pretty much everyone else has a hairline.
Does this mean Bart, Lisa, and Maggie are the only main characters who have blonde hair dispite the fact both their parents have/had brown hair?