I am not quite sure about poison ivy... but since we have tons of it around here, I assume all of those 3 leafed plants are it.
When I first moved here, DS #2 got a terrible rash after about a month. I rushed him to the pediatrician, as no OTC things had helped and he was in agony. She was quite incredulous that I didn't know this was poison ivy. I had to explain it was not exactly common in the desert.
I played in the woods constantly as a kid and never have had it. I suspect i might be immune to it, as DH has had it many times from working on our landscaping in the past couple of years, and I have had nothing.