I seriously would do tons and tons of outdoor of outdoor time. The best way to teach is by exploring. There is the BLUE sky outside with the WHITE clouds. The grass is GREEN or BROWN right now depending on watering-
. I water mine every other day and right in the middle is a nice big brown patch!
Anyway, the grass is SOFT the ground is HARD.
Things like that is so teachable and they get to learn while burning off energy.
Otherwise really don't worry about a "curriculum" at this age.