[dont_be_mean]

A plausible explanation I haven't seen suggested in this article is: lack of surprise.

This is slightly different than the divided-attention and lazy-parent theories.

There is evidence we learn more when we get answers wrong, not right. It's reasonable to assume then the more children you have the more right answers you eventually have as parent. And the same goes for a first child. You are both surprised when something goes wrong and you both learn from it.

The problem is, the parent doesn't necessarily need to be learning more as they have more children, so they take the shortcut of not letting younger children get answers wrong. They don't let them get surprised. Parents don't give younger children as many chances to screw up.

[balsam]

interesting. this would also imply that orphans grow up even smarter.