Police in Washington, D.C. typically issue a $100 citation for vehicles with tags that are expired past 30 days, though there can be instances where more serious measures can be taken. Since it's unlawful to operate a non-registered vehicle in the District, police can stop and arrest those drivers. Under the law, offenders can face up to a $1,000 fine and/or up to 30 days in jail. Predictably, this situation has raised the hackles of politicians and the American Automobile Association, which has called the practice "ridiculous."
In the case of the mother, police informed the woman that her children would be placed in the hands of social services if she couldn't find someone to watch them during her brief stint behind bars. She was able to convince a teacher to look after them.