I think we have poison ivy under a few trees in our yard, but, I can't be sure. Although it is in areas where my kids don't necessarily play, I don't want it spreading. So, if it is, how do we safely get rid of it. (We have a private well, so pesticides are not an option).
Prince George's County Maryland plant identification poison ivy poison ivy identification poison ivy look alive virginia creeper is not poison ivy wild blackberry wild blackberry as poison ivy look alive
Your first photo shows mainly Virginia creeper, a good native vine with 5 leaves in a whorl. Sometimes the whorls have less leaves, so it may look like poison ivy then. It is a useful ground cover in natural or not highly manicured areas. It produces berries that are great food for birds and it also has good fall color.
The small round leaves in the first photo are creeping Charlie, an aggressive non-native invasive weed. Pull it out before it gets in your lawn if you can.
The 2nd (at the top) and 3rd photos show a 3-leaved plant with fairly stiff stems that have little thorns. This is wild blackberry.
The 2nd photo at the bottom has some poison ivy. The leaves are shinier than the wild blackberry, and the stems have no thorns. You can easily pull small plants when wearing gardening gloves so you avoid the rash that contact can cause. Most people get an itchy rash from exposure, but are not highly allergic.
Birds spread poison ivy because they eat the berries. The seeds usually land under a tree. Pull them when the seedlings are young.
Here is our webpage on poison ivy: http://extension.umd.edu/hgic/poison-ivy
And our page that helps identify it: http://extension.umd.edu/hgic/identifying-poison-ivy