usually, a fine. How big, it really depends on the mood of the people in charge and where/who you are. If you are in the countryside, you might get away by paying tens of thousands of RMB (my ex-helper paid that amount after her 4th child. Oh, it also gets easier if you "sort things"out with the officials privately; she works in a big city as a domestic cleaner and can make several thousands, depending how hard she works and the clients she can snatch). If you are famous, have a high paying job, and don't want to humble, you could be fined up to several times your annual salary. There are also cases where you can be dirt poor and they still fine you and kick you out of a government job.

In at least one highly publicized case, by CCTV and the net, officials in an interior province did that forced abort atrocity when the baby was getting close to full term. No, I don't think those guys were sent off to a labor camp.

Don't think for a second this is universally enforced and that villages are full of single child crying their eyes out. Still plenty of families with multiple kids (whether they are registered with the officials or not is another question).

Gov't officials and State's company employees shouldn't have more than one, except when they fit the criteria of the new ruling; hence they have kids outside of China and bring them back with foreign passports.

The system is opaque and subjected to changes.