The entitlement in this thread to ultra-elite luxury goods is insane.
Penn State wouldn't even give me a merit scholarship, regardless of my (rather stellar) high school academic credentials, community service and social work, and extracurriculars (worthy of Ivy League admissions), so I was looking at the full 25k/year sticker price. IIRC, their honors college had even more tuition fees than the regular college.
UPitt also gave me a meager financial aid package and initially refused to honor their own UPitt Science Fair merit scholarship that they awarded me while I was still in high school for winning first place (they insisted it was already included in the "federal grant money"-only financial aid package that they gave me, though it seemed suspect, it felt like they "forgot" about it entirely until I called the right people; THEN I got my scholarship included as additional financial aid).
Especially in the latter case, I'm not sure where the entitlement was; I won a merit scholarship awarded by the state school, and then the state school "forgot" about it and then tried to substitute it with federal grant money.
I went to the Ivy.
EDIT: Staying on topic, on the note of the expense of having multiple children: My sister went to the state school, and it effectively tripled the amount of money my parents and I were paying per year to go to school (and it put all four of us in debt; I helped my sister out because I graduated before she did and managed to land a great software engineering job right out of school with a starting salary significantly higher than my parents' income -- I'm still paying off student loans four years later now).
We want to encourage the population to grow in sustainable ways, not only in some families that make having lots of kids a priority.
Now, the /parents/. They do have a choice. The general system outlined in Larry Nivin's science fiction universe where exponentially higher costs were associated with children past the first free one (there were also lotteries to fairly distribute most of the rest of the population sustenance quota, as well as the option of emigrating off of earth to unrestricted colonies).
Mostly, however, is the issue that today there are many who do not /have/ children because the imbalances in today's society make them feel unworthy or simply unable to do so.