At U9 I would rotate it.
The child who is already a natural organiser will still get chances to lead without needing the armband every week. Other players may surprise you when they are given a small responsibility.
I would also keep captaincy low-key. Let one player lead the warm-up, another help organise a restart, another welcome a new teammate, another speak at the end. That gives leadership more meaning than simply deciding who walks out first.
At that age I’d be more interested in what the children learn from the responsibility than whether the team has the “best captain”.
If one child always gets the role because they are already confident, the captaincy may simply reinforce what you already know rather than develop anybody else.
