I don’t know if this is a Lenten idea, exactly, because we’ve just started doing it now.
The kids got a little handout with 1 Cor. 13 on it… the “Love is patient, love is kind…” passage that eveyone likes so much for weddings. We decided to find the line that we do the worst, and work on that. (For us, that would be “Love is not prone to anger.”)
Still, I told them that the point of Lent was making a special effort to turn back to making God first, as a preparation for Easter. Easter celebrates that Jesus bought us eternal life, eternal life comes when God makes us into a new person, and becoming that new person means losing all the stuff about you that would make it impossible to live with you and still be in Heaven. Just as Purgatory gets us ready for the joy of Heaven, Lent gets us ready for the joy of Easter.
So, for Lent, you look at whatever you might let get between you and God (be honest: those are often the same things that get between you and your siblings!) or that you might be making more important than following God, and you work on that.
PS: Facing up to our backsliding by instituting the “Vice Jar” is a great idea! Personal amendment and giving alms, all rolled into one!