I'm very close to you, I have a 4 year old boy and a 2 year old girl, she will be 3 this December.
I have taken my boy out prairie dog hunting all summer, he loves bringing his bb gun and shooting at them, and it is an awesome opportunity to begin firearm safety. He loves doing it, and I don't have to worry too much because I know he cant cock that red rider bb gun quite yet ha ha. My daughter comes with us, but when we start walking she usually ends up on my shoulders, if she lets me pick her up ha ha....she is very independent.
I plan on taking both of them on my pronghorn hunts coming up later this month, and possibly a couple deer hunts, as long as we don't stray too far off of roads. But on my mountain deer and elk pack in hunt, or any mountain hunt where I cover several miles for that matter....They are staying with grandma. I would love nothing more than to take them, but where I will be hunting has bears, the kind with big humps on their back. And also, navigating through deadfall and steep mountains is a little bit much for either of them. They handle the desert plains pretty well, but mountain timber is too much.
Just take them on as many easy hunts as you can, squirrel hunts along an easy trail, prairie dog hunts, coyote hunts, and things like that. And make it as fun as you can, I notice that my boy works his butt off keeping up with the guys because he is enjoying it so much. And don't forget ear protection for the littles ha ha.