I gave my anecdote elsewhere, but I will recount it again. I felt embarrassed at age 23 to purchase a pregnancy test with my wife. This is simply due to cultural messaging saying babies are bad. Despite having been married for a year, making well above median wage and having enough for a down payment, etc, I was worried what others would think of me! And I come from a family that is very pro-child and pro-natalist for lack of better word. I can only imagine what my peers would have been feeling. I think in many people, it takes into their 30s for this feeling to go away, but if they wait that long to have children, they're having 1 or 2 max on average.
EDIT: I think many on here don't believe that there's anti-child cultural messaging, because they're in their 30s-40s where this pressure starts to go the other way. But if you start having kids at that age, on average, you will never have enough to hit replacement. To hit replacement TFR, the pro-child messaging must start at 18 or younger.