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.
It is true that before reaching adulthood children are a financial burden for society, but primarily they are a financial burden on parents. Tax breaks help make it more affordable and a viable option for more than just the wealthy.
But you seem to be of the opinion that having children is a selfish act that society should punish rather than encourage. Some people are not responsible enough to be good parents, or otherwise are not in the right circumstances where it would make sense. But generally children are an investment in society's future, and very much worth the costs of supporting with projected future contributions.
This is going off on a bit of a tangent, but you're absolutely right. Having children is the most selfish act possible. Nobody on the planet asked to come into existence; we're all here because of a choice our parents made. Regardless of your place in the world, no human experiences their entire life without pain and suffering. I am personally very happy with my life, but there have of course been ups and downs. By producing a child, you're guaranteeing that another person will experience suffering and sadness. Nobody lives forever, so you're condemning another person to death.
Having children (to some degree, not unchecked) is necessary for the human race to continue to exist, but the idea that producing and raising a child is a selfless act is as far from the truth as you can get. If you consider a theoretical world where everyone was suddenly sterile, the human race would cease to exist within a very short time. A lot of other things would cease to exist: Sadness and heartbreak, murder, rape, war, terrorism, poverty, starvation.
One might argue that brief periods of happiness give a reason for continuing human existence, but is this really true? Most people, if they're lucky, go through life in a neutral state; we might not be happy or sad, but we're "doing okay." If suffering is a -1 and happiness is a +1, with everyday life being a 0, then every person is going to ultimately average out to somewhere around zero. By having a child, you're making an irrevocable choice that you want another human being to live a life that's either neutral to a point that's statistically insignificant or predominantly negative, and you're making this choice because something in your brain is telling you to. It's the epitome of selfishness.
Breathtaking.