CHILD SUPPORT RETROACTIVITY
FAM. CODE 4009
An original order for child support may be made retroactive to the date of filing the petition, complaint, or other initial pleading. If the parent ordered to pay support was not served with the petition, complaint, or other initial pleading within 90 days after filing and the court finds that the parent was not intentionally evading service, the child support order shall be effective no earlier than the date of service.