A HS coach can coach a youth club, no rules against it.

KSHSAA prohibits a HS and/or JH coach to coach their team members inside the school year but outside the season of sport. So a HS/JH coach can't coach their HS/JH team members during the Fall or Spring when the team season is not in session.

In the summer, there are no restrictions about who you can coach and/or when.

I believe this is the rule.