If they start now, even if they are screwing it up now, think how good they will be at it when they get to be my age.
I have to remember I wasn't very good at this when I started.
Why don't genealogists remember that when we are helping beginners? I think it is because we all have poor genealogy (read bad source citations) from when we started that is still sitting there needing to be cleaned up. Or maybe we've gone through the painful process of cleaning it up. Either way, we want to save them the trouble.
But you can't save someone from going through the process of learning. I have to let them not do it the way I think it should be done. They have to learn. They may not be perfect. That's ok.
Otherwise I shut them down. When I go on and on about how to research, or laboriously show them how to document perfectly, they shut down. That's too much for a beginner. They have to see the fun of it--finding things, learning about your family. They'll have time to discover how to do it right--but only if I teach them to love it first, and not browbeat them that it has to be done perfectly.
I need to let them do it in a teenage way. They can do it in a 40 year old way when they get to be that age.