It would only be a problem if the child items need different types of information - for instance, if the parent row had columns for string, int, pixbuf and the child rows had int, int, string. In fact that might be doable, but let's see if that's what you need before getting into it.
Ok I see. One column should be fine for me. Itīs all std::string. If a child is selected I guess I can get the value of the parent, anyway with row.parent()?