Lesson #1: Do not schedule both a dentist appointment and a doctor's appointment on the same day for the same child.
Lesson #2: Do not leave your umbrella in the car during said appointments.
Lesson #3: Do not assume you'll have time to go home for lunch between appoinments.
Lesson #4: Do not allow your children to bring their own toys into waiting rooms (unless you don't want those toys to come home with you).
Lesson #5: Don't forget to take deep breaths.