The best part about having a kid is the way it allows you to relive all the best parts of your own childhood, and to do things you never got the chance to.
Having kids makes you stop into places you'd probably normally pass by. Circus tent? Well, the boys need to see a circus! Carnival ferris wheel in the distance? Get on over there and buy those boys a corndog and a lemonade.. take them on the tilt-a-whirl.. they deserve it.
You do things like buy season passes to Seaworld just because they liked the movie "Finding Nemo", and you sit through all the little shows for them... but really it's for you, too. Because you forget how much fun it is to climb the rope ladder of a pirate ship, eat warm cotton candy, or ride on a carousel horse... but the memories come flooding back pretty quick when you share those experiences with your little bundles of bouncing excitement.
You get to plan cartoon birthdays with bright and colorful decorations.. wander party stores searching for the right pinata... run around the toy department pressing all the buttons, excitedly searching for the right gifts, and dragging your husband away from the Star Wars section while reminding him it's not his birthday yet.. so drop the x-wing fighter. (Okay, maybe that last one is just me.)
Having kids is like having a license to be a perpetual Peter Pan. You get to be a goofball with impunity... and that rocks.