UPenn study (PDF) is a pretty good analysis of why birth rates are on the decline in Europe. There are many reasons, some social and some economic. Women waiting until later to have children, for example, is one reason. Another is the economic instability young people are experiencing. Costs of having children alongside difficulties getting stable housing or being able to buy a house are others. But I didn't really see where taxes were a huge issue.
Who among us decided to have kids because it meant we got a deduction for them on our tax returns? I promise you it wasn't even close to the first thing on my mind at the time.
Rick Santorum has a one-track mind. His pony is abortion and making babies. Preferably white babies. But even for Mr. Frothy, this one is a bit out in the twilight zone.