Emotional regulation can be tough for kids with mental health issues. However, it’s also true that some people, even kids, just aren’t the feeling type. Which is not to say they don’t have emotion, it’s just to say they lean more heavily on other cognitive functions.
The best way to help someone recognize and work with their feelings is to point out what you think they are feeling. Asking someone to tell you how they feel is an awkward question for all of us, especially kids. But if you say, “you seem sad right now,” and comfort them with a hug, you’ll really pull it out (assuming they were feeling sad, that is). Notice how my example didn’t offer any preaching about the sadness, and asked no questions about why. It’s best to mind your own business on why unless they offer it unprovoked. You can comfort someone without knowing why they feel what they feel. And, they will be much more likely to share with you when there’s no pressure to do so.
So, when you notice an emotion, acknowledge it with respect. This mean you’ll have to start with negative emotions since those are the most likely ones to expose themselves. If you see anger, tell him how healthy it is that he’s angry, point out some healthy ways to deal with anger.