Traveling by Plane: Exersaucer

Traveling with 3.5 Year Old, 1.5 Year Old, and 3 Month Old

We are flying to Florida in March (Spring Break). My parents own a vacation home there. I would like any advice you can offer for airplane travel, car seats, stroller, crib/sleeping arrangements, etc. We did not purchase a seat on the plane for the infant. We are flying American Airlines out of O'Hare to Ft.Myers. I have never flown with 1 kid, much less 3!! I am so nervous...HELP!!!