This here will give you a bit of info about it. Area 54 has been using it for a while now on his Giant AC
http://www.mtbdirt.com.au/modules.php?name=Forums&file=viewtopic&t=21783
I actually think you're less likely to injure the child in a stack... Any half decent parent would quickly cast aside their own safety and wrap themselves around the child in front of them creating a safety 'cocoon'... If the child is on the rear there is damn near nothing you can do about it. Certainly, the adults safety doesn't even warrant a mention when there is a child to take into account.
Matt.