I can’t fathom of a single non-government employee who would say “take it easy, I’m a ________” in response to such an accident.
But you are welcome to prove me wrong.
Have any links demonstrating otherwise? Non-government employee strikes a child and tells the child’s relatives to “take it easy, I’m a _______”.
So basically you believe the cop (or anyone else who accidentally hits a child) should be open to violence from family members.
And as an aside, I think you are taking the statement "take it easy, I'm a cop" in the worst context possible. You probably think he said it sarcastically when he very well could have been saying it to let the family know he could help the little girl. Or, yes, perhaps he was saying it in response to the violent overatures of the family. Either way, what the cop said did not justify the family's actions.