I've taken my 7 year old on day hikes for a few years now and recently started bringing my 3 year old along. I got the two of them to do a 2 mile loop a few weeks ago. It can be incredibly frustrating. Two kids and one adult is all about getting the kids motivated and moving at the same pace, which is almost impossible. But with just one kid, it's easier.

Still, a 2-3 year old just don't have an attention span to make much of a hike. I too have used my wife's Maya wrap sling to carry both of our kids when they were < 1 year old, but not now that they're bigger. A backpack carrier might work for the 3 year old, but I can carry him on my shoulders for at least half an hour at a time before he wants down. If I had to really move the two of them any long distance, I'd have to break out a jogging stroller for the 3 year old and I'd pretty quickly wish I had a double for both of them. I've had a jogging stroller over some pretty rough terrain, but they're all pretty worthless in soft sand.

I think the biggest thing is to get out and walk now with the kid. You'll learn what works for them. My 3 year old says he hates hiking but if he knows (or thinks) there's a water cooler at the end of the trail, he'll double-time it just so he can pour water on his head. My 7 year old can get bogged down picking up sticks or anything else within reach, but if I break out a stopwatch and time us between markers, she'll haul ass.