If you have two or more children, you have higher chances of children rivalry. I have a boy and a girl, ages 7 and 3 and they are very different individuals. I experience this a lot, both are very competitive and want to be number one all the time. People say sibling rivalry is normal and they'll work it out themselves. This isn't very smart! Make it a goal that they should be good friends or they'll miss out on the joy of developing closer bonds.
LEAD THEM TO KNOW EACH OTHER'S HEARTS. Conflicts begin when one feels you're taking side. Although one may behave better than the other, they should be treated fairly. Our responsibility is to create stronger ties, help them understand they are unique and value their differences. Build their sibling up (for all siblings), show them what makes their brother or sister happy or upset. Give them a hug or an "I appreciate you" note when you catch them doing good for their sibling. Play games such as naming food their sibling loves to eat or favorite things to do or "what I love about my sibling". Show them how to apologize by saying "Im sorry, please forgive me" and to grant forgiveness by saying "I forgive you because I love you." Do not allow tattling because it does not promote trusting relationship rather encourages hateful behavior.
LEAD THEM IN ADVENTURES, FUN AND SILLINESS. We make mistake of thinking, to raise good children is to have rules, orders, high expectations and punishments. But to truly impact their hearts is to create warm, loving relationship and provide a home that's fun, be silly, allowed to make mistakes, appreciated and corrected in respectful and loving way. As a result they'll treat their siblings in the same manner and creating happy memories together. When playing with them, set good example in winning and losing gracefully and do not allow teasing as it lowers self esteem.
LEAD THEM TO PRAY AND PROTECT EACH OTHER AND CREATE A RELATIONSHIP WITH GOD. God has called us parents to instruct our children in a way pleasing to Him. Creating a home in the Lord, talking about God, showing them how to pray and introducing it as a privelege to communicate with our Creator. Thanking Him for the love and good things they've experienced in life and to ask God to comfort them when they are scared and hurting. Because God answers prayer. When they learn to pray for one another, they will learn to look for each other with love and concern.