This blessing comes from the older Roman Ritualor Collectio Rituum from 1954. It has been revised since then, but the former one can still be used.
V. Our help is in the name of the Lord. R. Who made heaven and earth.
V. Our God is full of mercy. R. The Lord has care for little ones.
V. O Lord hear my prayer. R. And let my cry come unto Thee.
V. The Lord be with you. R. And with your spirit.
O Lord Jesus Christ, Son of the Living God, Who, begotten in eternity, yet didst will to he born in time; Who dost love the innocence of childhood, and didst lovingly embrace and bless the little children who were brought to Thee: anticipate the needs of this child (these children) with Thy tender blessings, and grant that no evil may corrupt his (her, their) mind, but that advancing in age, in wisdom, and in grace, he (she, they) may live so as to please Thee always. Thou Who dost live and reign with God the Father in the unity of the Holy Spirit, God, for ever and ever.
May the peace and the blessing of Almighty God, Father, Son + and Holy Spirit, descend upon you and remain forever.