Okay, I'll be the one dissident here!
We have a three year-old and we prefer to drive. The reason is, we go early in the morning and we invariably get to park within easy walking distance of the TTC and don't have to tram.
We like driving primarily for the easy exit it provides. Baby Girl can get pretty darn CRANKY at the end of a long day and we don't relish a wait at the bus stop.
Also, we sometimes go early, leave at lunchtime, nap and/or pool for a while in the afternoon, and then go back to one of the parks late afternoon/early evening. (should do that every day, but we never do) For that plan, driving is a lot easier than two round trips on the bus.