My DH lived near Orlando, so he's not as into Disney as we are. As a result, I take our 4 young kids (9,9,5,4) by myself sometimes. I always make sure to use some ID (mables labels, tag on shoes, etc.) that can be easily seen, and explain about finding a CM. I watch my kids like a hawk and we hold hands, but with 4 to keep up with, it's not easy. They can be there one minute and disappear if you look away for a second.
I haven't used leashes at the parks because my kids use the stroller more at WDW where there's more walking, but I have no problem with parents that do. After adopting my two older kids that were 3 months apart (like having twins) and having them run in different directions at once in shops as toddlers, I understand some kids need that measure because they can slip away from your hands like lightening. I got some ugly looks and comments for the 6 months I needed to use leashes with my older two kids as toddlers, but I wasn't about to let people who had no idea what I was dealing with daily keep me from doing the safest thing for my kids.