Can a referee sin bin or send off a player in Under 13 to Under 18 games?

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

• A temporarily suspended (sin binned) player re-enters when the referee permits. The referee is guided by the timekeeper if there is one. The player is not regarded as a substitute.
• A dismissed player can take no further part in the match.
• When a final caution is given, the referee records the offence and the time, and must quote them if the player is later dismissed.

SafePlay Code (Under 13 to Under 15). A penalty is mandatory after any breach of the Code. In addition, the referee may at their discretion sin bin or dismiss the offending player in the International game for 13 to 15 year olds.

The SafePlay Code does not state a sin bin or dismissal option for the 16 to 18 age groups, but the general misconduct powers in Section 16 of the International Laws apply to them.

Source: International Laws (April 2023), 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/