So this has happened to a family I know, not me, but it has grated on me.
A mum and a stepdad together since the kid was a toddler. The kid, now a pre-teen, alleges the stepdad hits him and yells at him. A referral is made to social services.
The mum sticks by the stepdad, says he can't possibly have done it. Eventually social services determine not sufficient evidence to take action and they think kid may have exaggerated or lied. So she now feels vindicated.
Bear in mind I've heard all this second hand.
If I had been in her shoes, I'd have ended the relationship. Whether it were true or not, if my child felt strongly enough against the stepdad to say this, there is a problem.
What would you have done?