Native Americans and poison ivy

[Beastly Despot]

A friend recently told me some Native Americans used to feed their babies poison ivy and if the had an allergic reaction, the babies were left to die.

Now, this sounded like BS but I looked it up on google and found some sites that said some Native Americans ate some poison ivy to develop immunity.

I wonder if anyone knows any more about this without me having to wade through a bunch of websites?

I guess allergic reactions to poison ivy would be a big problem if you were living in nature here in Indiana. The stuff is everywhere and I feel totally disabled when I get a good dose. How did those folks deal with that?