Them's is fighting words, correctly conjugated fighting words

So my children seem to have a fundamental challenge with it comes to conjugating verbs. Specifically, they can't seem to get things in the past tense. For many years I have let this go, probably to their detriment, but now I've started correcting them. So goodbye sweet little phrases like "I goed to school." I've enjoyed you. You've made me smile, but it is time for the little mokeys to grow up and conjugate.

Today at lunch the kids were fighting over a chair. (I may start having assigned seating at the table, because I think fighting over where to sit is insanely stupid, but that's a post for another day).

Anyway... So the fight went something like this:
Grace: Brynn, you stoled my spot!
Lisa: Stole
G: What??
L: Stole. You stole my spot. Not stoled, stole.
G and B: (repeating, tyring to get it right) stole
L: Right, so you would say "Brynn, you stole my spot."
G: But I thought you didn't want to hear us say that any more?
L: Well, I don't, but if you are going to say it, at least say it correctly.