That would be an encouraging statistic if it weren't for the fact that liberals reproduce not so much by having children but by recruitment. When conservatives send their kids off to college there is no telling what they are going to get back.
But I think that 20% figure already shows the rate of “conversion”. I know some would argue for 50% for conservatives’ kids and 0% for leftists’ kids, but it seems the survey has already taken them into account.