When people are free to WANT children and decide on how many, it's going to be 0, 1 or 2. Which might average out to 1.5 - 1.8 in most countries, far below replacement level.
There's nothing you can do financially to truly move the needle. Even people with no immediate financial challenges tend to not have more than 2 children.
Why not? Because a 3rd, 4th, .... adds no value whilst it does add immense logistical nightmares.
When you love children, 2 will keep you plenty busy. When you have 4 you'll have an issue with your car and home. You'll be spending most of your time driving them around to their schools, sports, hobbies, whatever.
It's not an economic issue, as tempting as it is to think that. When given the choice to want children, most still want them, just not many.