Personality and Intelligence
Like average babies, Maggie is impressionable and easily influenced by what she sees around her. She once hit Homer on the head with a mallet, shot a suction dart at his picture, and brandished a pencil in imitation of Itchy and Scratchy. See Itchy and Scratchy and Marge. Her talent for handling weapons is seen in Who shot Mr. Burns? and Papa's Got a Brand New Badge, where she is able to shoot a whole mob of gangsters with a rifle. Also, in The Monkey Suit, she holds up Marge for candy with a retractable knife.
She is however keenly aware of her surroundings, and can usually be seen imitating the flow of action around her. Like Bart, Lisa and Homer, she is not fond of spending time with her aunts Patty and Selma, attempting escape from the family car when Selma claims to want a baby.
Maggie appears to potentially be the real genius of the family. The episode Smart and Smarter suggests the possibility that she may have a higher IQ than Lisa (at least, she appears as extremely clever during the episode, even though her real IQ was unknown due to Lisa 'helping' her during the test as revealed at the end of the episode).
At age one, Maggie could spell EMCSQU (E=MC²) with her toy building blocks- as shown in the season one episode Bart The Genius- whereas Lisa at age three could merely spell "STAR" with hers. She's able to answer complicated questions putting cubes together (Smart and Smarter), and solve complex IQ problems. She's also able to count. In "Treehouse of Horror V", Maggie managed to spell REDRUM without anyone noticing.