Kids train for HYROX with two to three short coached sessions a week: easy running, bodyweight strength, and light practice of the race stations. Coaching quality and recovery matter more than volume. Loads stay light, sessions stay playful, and the race order gets rehearsed a few times before race day.
This is a direct answer from the CrossFit BC coaching team. Short version first, then the detail and the local context for training in Vancouver. If you want the same answer applied to your own situation, a coach will walk through it with you in person.
Our group classes are for ages 16 and up. Younger athletes train by arrangement in small-group or one-to-one sessions with a coach.
Two to three short sessions a week is plenty for most kids preparing for a Youngstars race, with rest days and other sports around it.