Two of my kids had poison ivy this summer, but luckily they didn’t react too badly to it. I used calamine lotion, threw them into the tub with some Aveeno oatmeal powder mixed in, and let them have some extra swimming time in the chlorinated pool.
My daughter came down with the rash first, and since none of us had ever had it, I googled it. There are websites devoted to all kinds of home remedies, but the scariest I saw involved rubbing straight bleach on the rash. Apparently it burns like crazy but helps…but at a cost. There were also stories of people who did that with bleach and ended up with even worse health problems. I wouldn’t suggest you do that at all, but if you have access to a chlorinated swimming pool, take a dip. If not, you could try adding a small amount of chlorine bleach to your bathwater—like, half a cup.
Out of all those treatments, my daughter said the Aveeno bath helped most with the itching.