Well, the first way to prevent would be to avoid but I have two small children and I might as well hold back the wind than curb their enthusiasm when outdoors. With that said, we can have both, a wonderful outdoor experience and a safe one by learning to identify poison ivy.
Poison Ivy has some distinctive traits but can be difficult to identify:
1) three leaves together
2) shiny leaves in the spring
3) reddish in the fall
4) Isn't supposed to grow in higher elevations so north of Lake Placid is a safe bet
1) In your car/backpack First Aid kit keep a bottle of isopropyl alcohol and some wipes
2) Direct contact is needed to get a poison ivy rash
3) Dogs are carriers so beware if you are in an area known for poison ivy
4) Isopropyl (rubbing) alcohol helps to dissolve the urushiol oil that causes an allergic reaction. There are commercial products that will do the same thing and perhaps be gentler on a child's skin.
5) With small children wrap their hands so they don't rub any oils onto their face.
6) The oils will need to be cleaned off any effected area within 10 minutes of contact.
7) Store clothes in a plastic bag until able to wash them. Contact with even the smallest amount of poison ivy can cause a break-out.
8) when you get to a place with a shower take a cool water shower with