Poison Ivy?

This morning I noticed Noah had some bumps running down one finger. We assumed it was ant bites because he's a fire ant magnet when outside! But, they went on to fill up with fluid and he scratched off the top of one. (Ever try to keep a bandaid on a 2yo's hand?) We've never had ant bites do that. I know he wasn't burned on anything and I can't see friction causing those blisters, so I'm thinking poison something?

Any ideas?