Our children are now 8, 6 and 4 -- and we still like to have a stroller handy in the car, just in case.
We have traveled with our own children plus several others, and have taken four European trips with this Urban Jungle Stroller from Mountain Buggy.
If all the kids were up to it, they all walked. It was handy to have a place to stow snacks underneath. If one of the older kids got tired, they could even sit a while on this one. (I'm even guilty of sitting on it... it's that strong... and I weighed 260 at the time.)
It folds 'fairly' small, but it is heavy at 21 pounds. Tires are big enough that they handle cobblestones great.
A stroller can serve many purposes when traveling with kids. In one instance, I misread a bus schedule and we had a ~2 mile walk from the a bus stop to our hotel. Our son, under 2 at the time, was lighter than my backpack (we traveled in one pack for all three of us -- my wife was pregnant) so... I put my backpack in the stroller, son on my shoulders, and the walk was easier on me.