Why is a youth team's player list hidden and why does joining need a password?
When the team's age group is set to juniors, the team gets two privacy defaults at creation: the player list is shown only to team members, not to visitors or search engines, and joining the team requires a randomly generated team password. This keeps the children's names from becoming public by accident and stops just anyone from joining.
A manager can change both via Manager > Team settings: the team password (“Public join password”) can be changed or removed, and the roster's visibility is set on the Settings tab with "Enable public roster". Share the team password with new families when you invite them, or add the members yourself: How are new members added to the team?. On parents and guardians: How can I add parents/guardians for players?