How do sin bins and send-offs work in Under 13 to Under 18 matches?

Under Section 16 of the International Laws (April 2023), for player misconduct the referee may, at their discretion, caution, temporarily suspend for ten minutes, or dismiss the offender.

• The power to suspend is not an encouragement to deal leniently with misconduct that merits dismissal for ten minutes.
• A suspended player re-enters when the referee permits. The referee is guided by the timekeeper if one is employed, otherwise the referee determines the end of the suspension. The player is not regarded as a substitute.
• A dismissed player can take no further part in the match, nor may they take up a position near the playing area where their presence is likely to provoke further incident.
• When a final caution is given, the referee records the nature of the offence and the time, and must quote them if the player is later dismissed.
• A team's minimum is 9 players. Players in the sin bin count as current participants, dismissed players do not, and the match is terminated if fewer than 9 remain.
• A "free" interchange is permitted if a player is fouled and injured by a player who is dismissed, sin binned or placed on report, but only when the injured player is immediately replaced.

Under 13 to Under 15. A penalty is mandatory for any SafePlay Code breach, and in the International game for 13 to 15 year olds the referee may also sin bin or dismiss the offending player.

Sources: International Laws, https://www.playrugbyleague.com/media/14513/nrl-international-rules-book-2023_web-version-1.pdf and National SafePlay Code 6-15 years, https://www.playrugbyleague.com/safety/safeplay/