California's child neglect law, Penal Code 270 PC, applies to any parent of a child.
This means that you can be charged with this crime even if you are not the custodial parent--or were never married to the child's custodial parent.
Also known as "failure to provide care," the crime of child neglect consists of failing to provide necessities for a minor child, willfully and without proper excuse.
Now, the requirement that neglect be "willful" means that you are not guilty of child neglect for failing to provide a child with necessities if you did not know about him/her--or if his/her other parent kept you away from him/her and you did not know s/he was being neglected.
But if you know that a child of yours is being neglected, and you do nothing to remedy the situation, you can theoretically be charged under California Penal Code 270.