DC18 and I can both be like that sometimes, albeit less so than as children. There were definitely times when DC18 would get into trouble at school in a bad mood and would not want to talk about it until he felt comfortable and safe. DC15, however, is as open as a book and is rarely moody. Some of it might be personality (DC18 and I being introverts) or overexcitabilities (DC18 and I fit most of them)...