My son and I will be arriving in Zurich on Saturday a.m. and explore the mountain regions Easter Monday. Is Easter Monday typically a busy travel day in Switzerland to the mountains?
The busiest travel days are by far from the plain to the mountains at the start of the holiday and from the mountains to the plain at the end of the holidays.
Most cantons have holidays one week before and one week after Easter. That means friday one week before good friday, and sunday one week after Easter are going to be awful. Easter monday is in the middle of most people's vacation so it'll be fine. Keep in mind that it is an official day off in most places, so it counts as a sunday for time tables. (For the major train lines this doesn't change much, for minor bus lines it does).