Welcome to another Daily Halacha. Can one speak Lashon Hara (evil speech) about a child? This question comes up many times. The answer is: it's Asur, it's not allowed. Parents cannot speak Lashon Hara about their children. Children also have a status of Amitecha, part of your nation. Therefore, parents are not allowed to speak Lashon Hara about their children.
However, obviously, if parents need to discuss what the child did in order to be Mechanech them, in order to educate them and help them grow, then, obviously, in such a case, it's Leto'elet, which means it's for a good purpose to speak Lashon Hara. You're not doing it to damage them. You're not doing it to damage your children in a negative way. Just the opposite. To the contrary, you're doing it as a positive, to build them in how to act and how to have derech eretz, how to have manners, and how to raise a proper child.
Therefore, there is Lashon Hara on children. But if parents disagree—if parents want to discuss what the child did in order for them to be Mechanech the child for their own benefit, for growth, and what the plan is for how to discuss something with the child—it's called Leto'elet for a good purpose, and then they're allowed to speak Lashon Hara. 99% of the time when parents speak about their children, it is most probably for Leto'elet, in order to enhance and how to build and how to educate the child in a better way.