According to a report by the National Center on Family Homelessness in 2014, nearly 2.5 million American children were homeless at some point in 2013. The U.S. Department of Education had reported that 1.3 million homeless children were going to school. California, which accounted for one-eighth of the U.S. population at the time, had one-fifth of the 2.5 million, which comes out to nearly 527,000. The relatively high cost of living and shortage of low-income housing, along with a largely stagnant minimum wage, are the more visible factors behind the gap.
The full essay is at "Homelessness in the U.S."