So ditch that guilt -- you're paying the price, after all, and making amends now, by helping your child through all those old hurt feelings. Besides, feeling bad doesn't help you act "good," any more than it helps your child. Here's your plan. Take it step by step.
1. Start with yourself. The "peace" in peaceful parenting comes from you. Specifically, from your commitment to regulate your own emotions. That means when you feel upset, you stop, notice the sensations in your body, and breathe. You refuse to act on that urgent "fight or flight" feeling that makes your child look like the enemy. Whenever possible, you delay taking action until you feel calmer.
This takes practice -- both in the moment with your child, and in general, as you become more aware of your own thoughts and emotions. It is really, really, hard. Every time you do this, though, you're building gray matter in your brain, which develops impulse control. And you're excavating those triggers, so you don't get upset so often. The result? A happier, more empathetic, more peaceful parent. (And role model for your child.)
2. Focus on Connecting. Positive parenting doesn't work without connection, because you squander your only leverage and have to resort to threats (which destroy trust and start your child acting out again.) So before you change anything else with your child, start building up your bond. Otherwise, you'll drop your punishments, but your child still won't feel motivated to "do right" and you'll just see more testing behavior. Start spending at least 15 minutes connecting one-on-one with each child daily, just following his lead and pouring your love into him. You'll be amazed at the difference in the way he responds to your requests.
3. Explain what's happening. Once you see more connection and better behavior, initiate a discussion. "You know how I used to yell at you and send you to your room when you break the rules? Have you noticed that I've been yelling a lot less? I'm so sorry that I've gotten into a bad habit of yelling so much. I love you so much, and I know you try hard. When you're upset, I want to help you with those feelings and with whatever problem you're having. I think you'll learn more from cleaning up your messes than from being punished, don't you? Let's work together to solve the problems that come up, okay?"
4. Ask for cooperation. "We still have all the same rules. Our most important rule is that in this house we treat each other with kindness. I'm going to work very hard not to yell at you, and to really listen and be kind. Do you think you can work on this rule, too, and be kind to your sister?" (It's best to limit yourself to the most important requests, at the beginning. Once you see improvement, you can work on other areas.)
5. Offer Support and Model Win-Win Solutions. "I know your little sister gets on your nerves sometimes, and she always wants to play with your things. That's really annoying to you. You deserve to be able to keep your treasures safe. But it isn't okay to yell at your sister or hit her. Why don't we work together to find a safe place for your treasures where your sister can't get at them? And if you start getting annoyed at her, what can you do instead of yelling?"
6. Keep setting limits. You'll probably become more flexible as you see it from his point of view more often, and that's a good thing. But you'll still need to set plenty of limits. The key is to set the limit BEFORE you get angry, while you still have a sense of humor and can empathize with his perspective. "You wish you never had to stop playing and get ready for bed, don't you? I bet when you grow up, you'll play all night every night! And right now, it's time for your bath." Acknowledging their perspective is what helps kids WANT to cooperate with us.
7. Expect emotions. When children have been punished, they've learned that those big emotions that drove them to misbehave are BAD, and so they try to stuff those bad feelings down. That doesn't work, of course. The jealousy, frustration and need are still there in your child's emotional backpack, popping out at the slightest provocation. The only reason your child keeps them under wraps is because he's afraid. So once you stop punishing, those emotions are bound to bubble up to get healed.
Acting out is not a personal challenge to you. When your child "acts out" he is acting out feelings that he can't express in words. Like "All those times you yelled at me, and I was so scared, I acted like I didn't care, but I was terrified inside....That fear is still inside me and it eats away at me and feels awful....So I lash out to keep those feelings down." No child could tell you that, so he acts out. Train yourself to see misbehavior as a cry for help. Emotions are never the problem; humans will always have big emotions. And, of course, that doesn't give him license to hurt anyone else. The key is to help your child work through the hurts and fears that are driving his anger, so they no longer drive his behavior.
8. Create Safety. When your child shows you her upsets, stay calm. Don't take it personally. The more you stay compassionate and accepting, the more she'll feel safe enough to show you the woundedness behind her anger. (Anger is just the body's fight response to those threatening feelings.) Expressing those tears and fears is healing. Once she shares them with you -- and she doesn't even need to know what they're about, or to use words -- those feelings will evaporate, and she won't need that chip on her shoulder to protect herself.
If she's stuck in anger, create more safety by being as compassionate as you can about what's upsetting her. If that isn't enough to help her cry, and she stays angry, it's a sign that she needs more daily empathy, and more daily laughing with you. Both build trust.
9. Help your child make sense of his experience with a story. "When you were little, I was having a hard time...I yelled a lot...I didn't know what else to do...That frightened you....So you got very very mad sometimes...But now I work really hard to be kind, and not to yell....You don't get so frightened....And you are learning better ways to show me when you are scared or mad.....We work together to solve problems in our family.....Everyone gets upset sometimes....We try to listen to each other and be kind....Then we always make things better between us." All children benefit from using words and stories to understand their emotional life. Just be careful to empathize, not analyze -- so he feels understood, not invaded.
10. Teach reparations. If you've been punishing, you'll feel unfinished if your child breaks a rule and you don't punish him. Train yourself to think in terms of repair, instead. So after everyone has calmed down and is feeling reconnected, have a private discussion with your child about what happened. Listen to his perspective and empathize. "You were pretty mad when he did that...I hear you."
Once he's past that upset, point out the damage: "When you said that to your brother, it really hurt his feelings....and it made him not feel as close to you." Ask your child if there is anything he can do to repair the damage. "What could you do to repair that hurt with your brother?" Resist the urge to punish or force an apology. Instead, empower your child to see that he can repair his mistakes. "You know we always clean up our own messes, and this is just a different kind of mess, like spilled milk....I know you'll think of just the right thing to make things better with your brother....I can't wait to see what it is." Just as with spilled milk, the process of cleaning up his messes will teach him that he doesn't want to cause those hurts to begin with.
11. Model apologies. Don't force your child to apologize, because it leads to resentment. But if you model apology yourself, your child will follow your example. When something goes wrong, take as much responsibility as you can. "I see two upset kids...I'm so sorry I wasn't here to help you work this out before you both go so upset and started hitting...and then I got worried someone was getting hurt, so I started yelling, too...I'm so sorry....Let's all try a do-over.....I know you don't want to hit each other, hitting hurts...And I hear how mad you are....Let me help you so you can tell each other what you need without attacking each other." Over time, your modeling will help your children step up and take responsibility, too.
12. Expect setbacks. You're human, so you aren't perfect. Have compassion for yourself, just as you do for your child. Expect to make mistakes. Expect some days to be a huge struggle. Parenting is hard, and this kind of parenting is even harder when you start. But it gets easier. And even while it's hard, and you're healing your child's old wounds--and your own--you'll feel the difference. Quite simply, there's more love, more often.
You're on a path now that leads to a happier, more peaceful family. Two steps forward, one step back still gets you where you want to go. Soon you'll find yourself in a whole new landscape. Enjoy the journey.