Yes. You are changing their environment. Dave

I have a variety of brassicas that I want to plant this weekend and have been hardening off my 6-week old seedlings for the last few days. They are up to 8 hours/day outside and will be staying out all night in a few days. My problem is our weather is forecast to be 100 degrees for a couple days mid-week and I'm worried this will stress the plants and/or cause them to bolt (?) Should I keep them inside during these very hot days or does that disrupt the hardening off process at all? The weather will cool to the 80's and then downward later in the week.

People need pictures to offer help.

My first thought would be wind too for the plants to wilt like that once outside. Even in a deep kiddie pool the wind isn't going go be entirely blocked- though it will help reduce the wind a lot. I wouldn't be the temps outside since 65 is around what indoors is unless it's a big change. OP. Like if in the house it's full light 68 with no air movement and outside it's 65 in the shade with some breeze that might make a tomato wilt a little. Not a lot or for very long, but it could happen. The pic of the plant does not look wilted at all, that looks fine. The leaf damage could be wind, or errant air liquids hitting the leaf. Random like bird pee or a drop of collection off a tree or structure that happens to blow over and land there. Sometimes a lonely raindrop or few falls randomly.