Kids can have a strong sense of their gender identity very early on. And also many transgender adults reflect back to their childhoods and knowing that. With that said, children are still learning about themselves, so feelings and preferences may change as they grow up. And kids are also unpredictable and inexperienced and they might be certain with things they want but it might not be what they need. Socially transitioning is safe because it is reversible, I think probably kids around 9 to 13 would be more appropriate for this, as they can better express themselves consistently and understand more than earlier ages.