I think childhood stuff is always worth discussing as a way to learn about a person. Your past experience is what makes us who we are. There doesn't have to be a major trauma for it to be valid. I think very strict solution oriented CBT places little to no emphasis on your childhood, but that's because it's usually targeting something very specific like a phobia and focused on the here and now. Most talk therapy takes a look at your childhood, or I think it should. Otherwise it's almost impossible to get a sense of the whole person.

You could bring it up by starting your session by saying "I've been thinking a lot lately about some things from my childhood and wanted to discuss with you" or something like that...