Airlines recommend you get to the airport 2 hours before your flight so you can check in and get through security. All that stuff has very rarely taken me two hours. Despite that, when I travel with my kids we give ourselves the full two hours.
The main problem with this occurs when it takes a half hour to get to the gate. Now what? We have so much stuff it is hard to chase the kids around but you want them to wear off some energy so they can site on the plane for the next couple of hours. Tampa International airport has a great solution, a playground in the terminal.
We went flew in and out of Tampa last week. We got to the gate with about an hour until boarding but not to worry, the kids played the whole time in a great little playground. They ran, climbed, jumped, laughed, and they were ready to go sit for a the 3 hour flight. Thanks Tampa, we are flying into this airport when we go to Florida!