The truth, the whole truth, and nothing BUTT the truth

Sometimes I suspect my kids are lying to me but I'm not quite sure.

Tonight was not one of those nights.

Taryn and Ashlin were getting ready for bed and Ashlin is trying to ditch her panties for her pull-up very discreetly.
Taryn: Mommy, I think I saw poop in Ashlin's bum.
Ashlin: It wasn't me!