It's not about judging. It's about making sure a child is okay. In that situation, personally, I would have called the police. I wouldn't have taken a child into my car, but I can see why your DH did. I would have asked the child all the right questions, stayed with them until the police arrived etc.
i think this is what i would have done as well. i also think of my DS at a couple of weeks of 2.5 & wonder if he would have picked the right house when going past or would have said yes to a house with something in the garden that looked like fun or just similar to our house?

i'm not sure how i would react if it was me but i think i would have so many feelings - relief, panic, concern, embarrassment that i might have reacted in a way that people may have thought strange.

as for reporting to DOCS, i think go with your gut instinct. or you could call the cops, tell them what happened & say you're not sure whether you should do anything else & let them give you some advice