Actually it is not a typo. When used in the possessive case (with apostrophe) it is very common. For example, "Children's Medical Center in Dallas" owns Childrens.com.
There are probably hundreds or more of "children's hospitals" and care clinics throughout the US, so possibly some children's clinic in the US might want the domain.
The quoted results in google for "childrens" returns 13,900,000, obviously in the possessive case.
When you look at adword support on Google you find that there is *heavy* advertiser competition, and strong search volume. So the phrase is in very common usage, widely searched, and has heavy advertiser support... sounds like a good mix to me! Obviously, the possessive form "children's" has higher search volume than the grammatically incorrect version of the possessive "childrens".
I have taken a few weeks off from watching the drop lists, but had I seen it during my drop scan I would have picked it up... or at least tried in the auction after the drop catch.
Just out of curiosity, did you hear President Bush use the "childrens" phrase... which was grammatically incorrect as used, but funny.
Good find.
Marc