He wasn’t asking about food without a proper hechsher.
I’m taking my chances that he’s asking about kibud av v’eim because it’s a personal grievance.
Also, parents are often the least likely to have a positive effect through scolding, especially parents who aren’t treated respectfully.
I think the OP should be asking what he can do to improve his relationship with his children, not what he can do to improve their behavior.