As is stands, parents are able to claim their children as dependents on their tax returns, which lowers their overall tax liability and in effect means that the parents either pay less in taxes or receive a higher return at the end of each year.
Until they reach the age at which they can work, children are a drain on society. They receive public schooling and receive the same benefit from public services that adults do, yet they contribute nothing in return. At the point that they reach maturity and are gainfully employed and paying taxes, they become a functioning member of society.
If a parent decides to have a child, they are making a conscious decision to produce another human being. They could choose to get a sterilization surgery, use birth control, or abort the pregnancy (assuming they don't live in a backwards state that's banned it). Yet even if they decide to have 15 children, the rest of society has to foot the bill for their poor decisions until the child reaches adulthood.
By increasing taxes on parents instead of reducing them, you not only incentivize safe sex and abortion, but you shift the burden of raising a child solely to the individuals who are responsible for the fact that that child exists.
I am a strong advocate for social programs: Single-payer healthcare, welfare programs, low-income housing, etc, but for adults who in turn contribute what they can. A child should only be supported by the individuals who created it.
Children are not a drain on society, they are society. You cannot have a society for longer than a single generation without children. They are critically important to continuing any society and penalizing people for deciding to have children is backwards thinking.
The idea that a single family body should be the sole people responsible for the development of a child is also a foolish and somewhat modern misconception. The adage of "it takes a village..." comes to mind. As a society, it is our collective duties to ensure that all members of the society are healthy and cared for. We are communal, social creatures who have long relied on community to be successful and raise our children. This individualist perspective is myopic and counterproductive.
Additionally, the value of a human being simply cannot be reduced to what they contribute to the GDP. Children or adults.
Also the idea of yet another way or reason to exclude young people from society, yet another way to make them other or less than is the opposite of what modern society needs, and should be treated as fundamentally offensive.
Nowhere did I suggest that people should just completely stop having children. The fact is that children are extremely expensive, and having more than one per adult is quite frankly unnecessary. At least until the unchecked population growth is under control, reproduction should be disincentivized as much as possible, and society should not be forced to bear the brunt of parents' poor reproductive decisions.
Overpopulation is a myth that results in supporting eugenics.
This is so wrong it's not even funny. Look at CO2 emissions and climate change. Do you really think we'd be destroying the environment the same way we do now if industry wasn't producing products for billions of people?
These can be addressed in ways other than eugenics. What you've suggested here is essentially that. And it only penalizes those without money. The rich can have as many kids as they want.