"Since the 1980s, an estimated 200 million Chinese live outside their officially registered areas and under far less eligibility to education and government services, living therefore in a condition similar in many ways to that of illegal immigrants... There are around 130 million such home-staying children, living without their parents, as reported by Chinese researchers."
Of course if the Chinese government was less secretive and obsessed with control, we could probably find more accurate statistics. But then this is the country that tried to discourage the US embassy in Beijing from posting accurate air pollution metrics because they were so embarrassing.
Veering slightly off-topic here, but in addition to what you said, the limitations on internal migration (for Chinese citizens) are absolutely insane by Western standards. Imagine that you couldn't attend school or obtain a driver's license or even legally reside in California despite being born there because your parents were "registered" as Illinois residents and moved without permission. As someone who rarely has to deal with any government agency more oppressive than the local DMV office, I can't imagine living in a country with that level of control over my life, even if they were handing out citizenship papers freely.
The other line moves faster.