Here's a Collect I wrote for use on this occasion.
O Lord our God, creator of heaven and earth, through your Son Jesus Christ you have revealed yourself as a heavenly Father to all of your children. Bless, we pray, all earthly fathers. Strengthen them to nurture, protect, and guide the children entrusted to their care. Instill within them the virtues of love and patience. May they be slow to anger and quick to forgive. And through the ministrations of your Holy Spirit, may all fathers be strong and steadfast examples of faithfulness, responsibility, and loving-kindness; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.