In all of the cases, the would-be kidnapper, a white or Hispanic man who appeared to be in his 50s, drove alongside the victims and offered them rides as they were walking home from Emerson Elementary School, according to San Diego police.Each of the girls -- two of them 10 years old and two 11 -- refused to get into the sedan, at which point the man offered them money to do so, SDPD public affairs Lt. Andra Brown said."When the girls again declined, he yelled, 'Get in the car now!' The girls ran away and were unharmed," Brown said. "In one case, the (man) followed the girl to her yard."On two occasions, the man approached a girl walking by herself, and on the other he approached a pair of them. The first crime happened on May 15 or 16 -- the victim was unsure which -- the other two on May 21 and May 23, Brown said.At Emerson Elementary School Friday, there were extra police officers and other precautions on hand. "It is very frightening," said Maria Corrales, whose 10-year-old daughter attends Emerson Elementary. Parent Alma Herrera added, "It's sick. It just makes me sick." The girls told police the perpetrator had a thin face with prominent cheekbones, wrinkles around his eyes, short "salt and pepper" hair and a white beard with a slightly darker mustache. They described his car as red and shiny, possibly a Mercedes four-door, with tinted rear windows and passenger-side front-end damage.Police have released an artist's rendering of the man based on the victim's statements.Despite the raised awareness, Fernando Sosa's son still wants to walk to school. "No way. He's asked me many times to walk alone and I've told him no because I know there are crazy people like this guy," said Sosa. Anyone with information about the abduction attempts is asked to call San Diego County Crime Stoppers at (888) 580-8477. Tipsters may remain anonymous and could be eligible for a reward of up to $1,000.