God gave your children to you, and He doesn't want them to grow up thinking they are useless or doomed to failure. They are valuable in His sight (as are you), and one of the responsibilities we have toward our children is to help them realize this. The Bible says, "Fathers, do not embitter your children, or they will become discouraged" (Colossians 3:21).
How can you overcome this? First, ask God to heal your past. I don't know what impact your parents' negativism had on you but whatever it was, ask God to help you forgive them, and to realize that He loves you and watches over you. He loves you so much that He sent His Son into the world to enable you to be part of His family forever. Have you committed your life to Christ? The Bible says, "How great is the love the Father has lavished on us, that we should be called children of God! And that is what we are!" (1 John 3:1).
Then ask God to help you go out of your way to support and encourage your children. Thank them when they help you; praise them when they do well; let them know you love them, no matter what they do or how well they do it.
Most of all, point your children to Jesus Christ and His love for them. We parents aren't perfect but God is, and even when we fail, our children have a Heavenly Father who never fails.