You can have a kid double rostered.
But if you have a varsity kid play in a JV game, you become ineligible for the jv playoffs.
Also, if your kid gets pulled up for a varsity playoff game, that counts as being a “varsity athlete,” per the transfer rules/penalties.
Why would anybody roster a varsity kid on JV if playing that kid on JV makes them ineligible for playoffs?
Is there a beneficial scenario?