When are kits out of danger of being "stomped?"

[MidwestMatthew]

Our kits are 12 days old and seem ready to leave the nest. I'd like to remove the nest box (leaving nest materials in the corner) because of the high temperatures expected this week. However, the mother rabbit has already shown disregard for the babies (jumped off the top of the nest box onto them a few times, requiring some modifications to the box) and I'm concerned she'll just run roughshod over them if they're not in the box.

At what point do the kits become reasonably low-risk of being stomped to death by Mama?

 

[Zass]

To date, I have never had a kit get stomped or trampled to death.
I do usually leave the boxes in place until the kits abandon it. I don't really think that is the reason they haven't been trampled though.
I've probably reduced the likelihood of losses much more by selecting for calm, even tempered does.