I started a junior group about 14 years ago. Started as an informal way to entertain a couple of kids before their parents XC crits.
Evolved over the years to a very structured weekly skills and fitness session (over the DSL period) called Dirt Critters where it’s now capped at 100 kids a term, spilt into 10 groups of 10 kids based on age/skill with 2 leaders per group, most with at least basic coaching tickets.
For ease of compliance and insurance/liability it’s now all run through AusCycling as part of the MTB club I’m part of the committee of.
Kids must be AusCycling members to take the risk off us. Leaders have WWCC and carry first aid kits. The world has changed in the last decade. Make sure you cover your and everyone’s arses. Cost is $20 per term, which all goes into fruit for after the sessions and end of term pizza/BBQ.
The most important thing though, make it fun, mix it up, and try to change around your location and activities. Skills are important to learn but if they aren’t having fun also, you’ll lose them. We have 3 different venues we move around. We restrict it from ages 4-14. Older kids can choose to stay on and assist with the groups. Many kids do it purely for the social side, plenty get the bug and race as part of our junior DH event (Mini Muddies) ran last month, and move onto (or additionally) the main ClubMud King of Ballarat series, Round 1 was the weekend just passed. We had like 10% of the field racing u13 and about 25% of the field entered as u15. The Junior racing scene is HUUUGE in Vic, assume it’s the same most places.
Also, obviously, make it inclusive. Close to 1/3 of the Dirt Critters are girls, and they love it. Many have gone onto racing club, state and national DH events after moving through the program.
I’d direct you to the FB page, but for obvious reasons, it’s private. I’ve moved on from it this year, with other MTB club duties taking my time up too much, but really miss it and the sessions.