"I don't know why" seems to be DD's go-to response when she's done something wrong. In the case of today, I found a large bag of macaroni spilled all over one of the cupboards. It's not near other food that she would have been getting, so it wasn't an accidental spill while getting something else. I ask why. She says she doesn't know why.

DH "demands" a why. I know it's pointless, but I still (somewhat stupidly, I'll admit) ask her why anyway. "It was an accident while I was doing x" would be fine if truthful.

She has ADHD and new meds are working better, but I think this was done within this last week, when she was already on new med.

So, if you have a "I don't know" kid, how do you deal with it?