I'm Doug, and I'm very sorry to hear of your son's situation. My goal is to provide you with excellent service today.
While it is legal for CA police to hold your son, and not allow you to speak with him for a couple of hours, generally the policy of most police departments us that the parents are notified of the detention of their child soon after the detention and transport to the holding facility.
Parents have no legal right to speak with their children who are detained by police---unless that parent is also a n attorney and representing their child. Eventually though, the police always allow access except in some instances of serious crimes.
Your son's alleged offenses are actually pretty serious, and legally constitute sexual battery
. The fact that he did this to 3 separate girls makes it even more problematic.
However, presuming this is his first offense, it is highly unlikely that he will be sent to juvenile detention. He will most likely be given probation, and if old enough, ordered to do community service. Here is a link to a legal discussion of sexual battery in CA:
You may reply back to me again, using the Reply to Expert link, if you have additional questions.
I wish you the best in your future,