I had that issue all the time. Kids are six years apart, so not fun dealing with two schools. The pick ups were ten minutes apart- be in the first few cars for the first pick up, and then for the next one, be late ;-) If you picked up older one first, you can pull your car into the drive through pick up while they go get the younger one- and if it's the older one waiting, they love every extra minute they can with friends.
I am dealing with two school districts this year and not looking forward to the elementary/ high school drama starting Wednesday. Pick up is ten minute apart, and the drive is 20 mins apart. But the good thing is, older one waits.
We had a rough summer - everything was poorly planned, poorly executed. Fire fighting mode almost all the time, no fires contained. Everyone had their own set of issues..
Advice to people with young kids: Take that damn vacation. You are never too busy.