Fathers are expected to be strong, so I made Mr. Incredible super-strong. Mothers are pulled in 20 different directions at once, so I made Helen, [as] Elastigirl, have stretching powers. Teenagers are insecure and defensive, so I had Violet’s powers be invisibility and force fields. Ten-year-old boys are energy balls, you know, so I had Dash have super speed. And babies are unknowns, so they could have no powers, which is what Jack-Jack has for most of the first film, or they can be a Swiss army knife of powers.
Source: latimes.com – Los Angeles Times