John: "Mary, do you know what mercy is? It is when I hit you and you say, 'I forgive you anyway.' That is mercy."
I started crying while driving! (And, of course, it was funny because he wasn't quite magnanimous to think of the scenario of granting mercy to his sister for hitting him.)
I can't recommend highly enough "24 Catholic Songs for Children" for Catholic parents raising little ones. It's amazing the catechism that little ones can memorize (and that power of memory is why we guard so carefully what our littles see and hear). John already has a nascent concept of the trinity, in that I'll hear him singing to himself, "The Father is God, / And the first person of the blessed trinity, / The Son is God, / and the second person of the blessed trinity, / The Holy Ghost is God, / And the third person of the blessed trinity."
And don't get John started on the story of Daniel and the Lion's Den! He gave his Occupational Therapist a lengthy explanation of how Daniel was "willing to die" (John had asked me many questions about what "willing" meant) and what martyrdom is.