There's no "suddenly" involved here. Not in the least. For hundreds of years in common law jurisdictions, judges have had the unilateral authority to jail a person who is in civil contempt of court. Neither jury nor "prosecution" need be involved.
Recent (in)famous examples of judge-ordered detention for civil contempt have included (a) the jailing of Bill Clinton's girl-buddy, Susan McDougall, during the Whitewater investigation; and (b) the similar detention of NY Times reporter, Judith Miller, during the Plame-Wilson contre-temps.
You can maintain as long as you want that civil imprisonment for contempt is a criminal prosecution. But you're basically butting your head against a brick wall. All the complaining in the world is not going to change the crystal-clear and long-running distinction in common law between civil contempt and the criminal law.
Yes, it is true that courts have always had a limited authority to order incarceration as a civil case, but only to prompt compliance with the orders of the court. That is a key distinction in determining whether a contempt charge is actually civil or criminal, as delineated in Gompers vs. Buck’s Stove & Range Co, 221 U.S. 418 (1911). For the charge to be considered a civil charge, the penalties must be remedial in nature, designed to coerce the defendant to comply with a court order. If they are punitive in nature, then it is a criminal contempt charge.
So, is incarceration for failure to pay child support remedial or punitive? The argument that it is remedial relies on the fact that it is imposed in cases where the defendant has defied a court order, namely the order to pay support. However, unlike other remedial incarcerations, these penalties don’t continue until the order is complied with. They have a set maximum term, after which the defendant is released whether they comply or not, just as in criminal contempt cases. Also, they can be applied retroactively simply for late or missed payments, even if the defendant has subsequently fulfilled his obligations by the time the contempt charge is issued. Those facts demonstrate the punitive nature of these charges, and if the charges are being used punitively, then they are rightfully termed criminal contempt charges, whether the courts call them that or not.