Because I was a terrible father, my children reject me. What can I do?
I would encourage you to never give up. Do not let their actions cause you to become bitter and then resent them. Remember, they were wronged by you. They may be wrong now, in how they are treating you, but they feel justified and probably are afraid to let their guards down and risk being hurt again.
If you already have admitted your faults as a father to them and asked for their forgiveness, you have done your part. You just need to continue living as though you are anxious to be a part of their lives. If you haven't, then you need to do that. Go to them in humility and explain the ways that you now realize they must have been hurt. Then, ask them to forgive you.
Since you know the Lord, you know what it is like to have a loving and gracious Father who is attentive to your every need; they may not. Be praying for them. Ask the Lord to show them His character and to give them open hearts to receive your efforts toward them.
God is about restoration. He desires that your family be in loving fellowship with each other. Just put it into His hands and then be patient for Him to work. May God bless you and your family.