If you want to increase births, you can't just ask couples to have children.
You have to change our social model. Right now, women "finish" their education some time in their 20s. They might have a boyfriend, but even if the do, they don't necessarily want to settle down and have kids, they have a student debt to pay and a career to establish. And of course, in the meanwhile, they might have 2-3 relationships (or more). Or none. By the time they find someone, they might be in their thirties. Then they might have one-two kids.
Then they break up.
So they woman might be like 38 years old, with two small children. Does a woman in this position really want to "start over" with another man?
And that's if she's not already sterilized.
Our social model is not designed to optimize fertility. Quite the opposite. Children are a bit of a drag, and they need to be produced at precisely the right time, or else they're unwanted and get aborted.
Really, what we need to do is encourage women to marry in their early twenties, have kids and then proceed to have an education and career.
You can talk about babies in sex ed, but if women plan their futures in terms of their education and career first, they're not going to think about about more than two kids.
We also need to talk about stable marital relationships.
That's really the kind of sex ed we need.