You don't have to bring it in, it will be fine.
Juniperus procumbens is tough.
How old is your son? If he's on the younger side, he might lose interest for a while and come back to a dead plant because playing outside is more fun than thinking of watering. This happens, it's not a big deal. Juniperus procumbens are easily found in a lot of nurseries and they are not expensive when bought as a garden plant. In a single repotting, the new tree will be at the same point in development as yours is now.
It might be fun to grab a couple and see how far you can push them together, as an experiment to learn a bit about the species without touching the important first one.
Have fun!