Need to make reservations in RV parks?

[TNTSR]

We are taking our 3 kids the 19th of December to sequoia, Yosemite, Grand Canyon, Zion and more places, but I wanna know if we have to make reservations to stay close to the main places, do you think is gonna be crowded? Thanks for your replies

 

[MemoriesByTheMile]

Check with each location you are considering a stop. They will tell you how full they are currently booked.

Being the off-season, and colder weather I expect they will have room.

If you were going in summer, that is fully booked around a year in advance in those popular national park areas.