Since most children survive to reproductive age independent of the parents abilities, I would suggest we are selecting towards simply having more children.
The evidence is against your statement, I think. Places that have the highest survival rates also have the lowest birth rates. On the other hand, the opposite is also true. Where we see lower survival rates, we also see higher birth rates. Some countries with high survival rates have had their native birth rates drop below replacement levels. The U.S. is barely positive--which I attribute to immigration from countries where the survival rates are still low by comparison. Culture takes some time to adapt.