Why do brothers and sisters fight?
Here's the answer:
Brothers and sisters fight when they want their own ways.
All of us are sinful; none of us is perfect. So we all displease God, doing wrong things, like when we bother our sisters and brothers. These things get us into trouble and cause fighting and arguing between the people who should love each other the most.
God gave us rules for how to live in the Bible. By following those with His help, we'll get better and better at getting along with other kids, including our brothers and sisters. The Bible teaches that we should put others before ourselves and give them good things we'd want them to give us. Try doing kind things for your brothers and sisters: making her bed, giving him the biggest piece of cake, sharing your favorite toy, and spending time doing what they like to do. Do these kind things, not so they'll do kind things back but so you can show them God's love.
Ask God for strength to be patient and kind to your siblings. Forgive them (or ask for forgiveness), remembering that God has offered forgiveness through Jesus' death on the cross. If you have trusted Jesus as your Savior from sin, you can show your siblings kindness so they can see how Jesus has changed you. You can't make them be nice, but you can control how you react to them.
"My dear brothers and sisters, pay attention to what I say. Everyone should be quick to listen. But they should be slow to speak. They should be slow to get angry. A man's anger doesn't produce the kind of life God wants" (James 1:19-20).
"So let us do all we can to live in peace. And let us work hard to build each other up" (Romans 14:19).