Another story here, with more details:
http://www.signonsandiego.com/news/metro/20041112-9999-7m12pinata.html
People-smuggling ought to be added to the list of traffic violations. The smugglers should be required to pay a large traffic fine if they can't be prosecuted for immigration violations. Red light violations and carpool lane violations are at least $271, and people-smuggling is much more dangerous.
Even without a change to the law, they should have been cited for driving with two children under 16 not wearing seatbelts. The fine is several hundred dollars for the first offense and at least one point on the driver's record. The 4-5 year old child might have qualified for the 6yrs/60lbs requirement for a booster seat, too.