Ron,
I've bushwacked many a time with mine, who are now 5 and 9. There is definitely a correlation between bushwacking and ticks. You'll get them either way, but not to the same extent by any stretch of the imagination.
My son has been going out with me since he was that little. The best prevention I have found is to have him ride in a backpack on your back. We have one that goes up to 60 lbs. Follow usual dress precautions, pants tucked in socks, shirts tucked in, and light colored clothes. And have him wear a little moab hat, lite color---REI sells them. My kids love theirs.
Cut his hair really short so you can see them--that helps so much. I just buzz Joseph's hair to about 1/4" in summer so I can spot things.
There are organic all natural insect repellents that are helpful but far from completely effective. Beats pure DEET on a kid if you are vigilant with checking them and take all other precautions.
This may sound strange, but be sure to check their ears, belly buttons, underarms, and their private areas. Ticks like those warm areas.
The other thing, don't concentrate on looking for ticks or chiggers or you'll likely miss them. Look for moving spots of dirt.
And with the little ones, try to stay on wider trails if you can--not little deer paths.
When you remove ticks, try to get all of the tick out. If you don't--don't mutilate the poor kid trying to. It used to be we took them to the doctor to get out the mouth piece or whatever if you didn't get all of it. Doctors don't do that anymore. Your body will recognize it as a foreign substance and over the course of a few months will get rid of it on its own.
A tick bite, even if caught quickly, can itch for up to a year with a small bump.
I always take spare clothes for the kids. Once Kristen had so many on her--literally hundreds-- that it was faster and more effective to change her. There is no way we could have gotten them all off of her. We put her clothes into a garbage bag and right into the washer.
Just some suggestions from my experience.
Renee