How do I fight LA Child Protective Services charges of child abuse?

My son’s mother reported me for child abuse because when my son went back to her after being with me he had a black eye. He’s just learning to walk and he legit fell onto the edge of the fireplace and caught his eye. Now Child Protective Services (correct name for Calif.) is saying they want to come to my house and interview me but my family is telling me I should not talk to them without a lawyer. I have a security clearance for my job and if anything like a child abuse charge shows up on my record I could be fired. My ex is telling me that until this is ‘cleared up,’ I can’t see my son. Should I talk to the protective services people without a lawyer and what if they do charge me with abuse?