Politicians this election cycle have been talking a lot about increasing tax credits for children, but offering a large tax deduction would actually be a better policy if the aim is to encourage higher birth rate among those who are economically responsible.
A tax credit would most heavily benefit the lower class (because it grants a set sum of free cash regardless of income), but a deduction would more selectively target the middle class. A $20000 deduction per child, for example, would eclipse the standard deduction after the second child. It would essentially eliminate income tax for most middle class families who have 4+ children.