This isn't a "don't teach sex to third graders" bill. If Florida teachers were spending too much time talking about sex to third graders, it would have been a totally uncontroversial decision at each district level to tone it down to an age-appropriate level. We don't have a "Don't teach integrals to third graders" law, after all.
This is basically "Mrs. White can no longer explain to the kids what it means that Timmy has two moms and why it's okay for Timmy" bill. Anyone saying "But why do third graders need a sex education?" are missing the obvious, maybe intentionally.