I have an almost 2 yr old who can walk 1 mile each way to one of the parks in the neighborhood. I've never timed it, but I think it takes us 30 min to walk each way at his pace. He does fabulous, and still has energy to play like crazy at the park!
I have a 15 mo that just started walking 2 months ago. I have just recently started taking short walks with her walking, and she can only last around the block, it's about 0.4 miles. By the end of this walk, she starts to let go of my hand and sit down! LOL So I know she gets tired just from that short walk around the block.
With the combo of ages you wrote down; I think a double stroller would be sufficient. I would say any child ages 22 mos and up would be fine walking, even the longer distances.
TIP: I have a mommy hook on my stroller; and I use that for the 23 mo to hold on to during our walks. It works so well! It creates a nice handle for him to hold onto, and it's flexible (moves in all directions on the bar) to allow him to adjust his pace or correct his walking without falling. He holds on the entire way. And when the stroller stops, he even stays there until I tell him he can go play.
