Before anything else, a truth that never changes: Jesus loves you today, stain and all, the exact same amount He loved you yesterday. He doesn't love you less when you mess up. Now that we've got that firmly in our hearts, let's talk about the stain.
Have you ever gotten your clothes stained with something that just wouldn't come out? We scrub and scrub, and sometimes it only smears the stain around, right? Then you need someone with the right soap to get it out. Our hearts are a lot like that. Everybody messes up, no exceptions: kids, parents, grandparents, everybody. Nobody manages to be perfect, no matter how hard they try to be good. And we can't clean up the wrong things we do all by ourselves.
But there's wonderful news: Jesus cleans. When we tell Him what we did wrong, with a truly honest heart, and ask for forgiveness, He really cleans it, and He doesn't keep bringing it up later. The first step is the most important one: admitting the stain is there. Whoever pretends to be clean stays dirty; whoever admits it and asks for help comes out washed.
Nobody can remove the stain on their own heart. Jesus washes whoever admits they need it.