If conservative parents have been having more children than liberal parents for the past few decades, then why hasn't the voting population become more conservative since Reagan was president?
((birth rate of pro-life families) * (rate of (children of pro-life families) that are pro-life)) vs. ((birth rate of pro-choice families) * (rate of (children of pro-choice families) that are pro-choice))
Is this a joke? We just finished one of the most pronounced conservative swings in American history, with all 3 branches of federal government and many local governments all under Republican control. How much more conservative did it have to get to convince you?
The Republicans really had to do massive amounts of damage to get Obama elected and break the trend. His election does not, in and of itself, prove that the U.S. has decisively shifted away from conservatism. If he is perceived to have some success, it might, but it is still to early to say for sure.
Anecdote != data.
There are "defections" in both directions.
Even if kids have the same values as their parents 51% of the time, you'll see the effect.