Or, all the planning goes out the window when one of them is wailing or throwing a tantrum, or is so so so eager to show you this wonderful thing they finished drawing for you. Then you have to adapt that wonderfully planned schedule/plan, so your previously-allotted buffer dwindles and next thing you know you're one new-issue away from being late.
But yeah, one of other comments mentioned. There is a difference between being late once in a while vs always.
Yes, being a bit early sometimes is a natural consequence of leaving enough time so that you're not late. Being late is much worse than being early because it is disrespectful of other peoples time.
If you're a bit early, then you get a few stress free minutes to hang out with your kid: sit in the car and sing songs together, run around the school yard, take a walk, talk about whats been on their mind lately etc.