Parents are extolled in the Old Testament to bless their children. It is actually highly recommended in the CCC for parents to bless their children daily, or at least on special occasions.
Bear and I used to bless our eldest before bed using a blessing that parents were told to give to their children found in the old testament adding the Sign of the Cross at which point we'd trace the cross on her forehead with one's thumb.
NB: This was usually bestowed before bed, obviously
May God bless you and keep you.
May He let his face shine upon you
May He send flights of angels to protect you in your sleep.
In the name of the Father, and of the + Son, and of the Holy Spirit Child answers Amen!
I found another blessing similar but the child is named in my New Saint Joseph's Missal (2012-13), thought I would share.
Bless N, and keep him/her in your love.
Grant him/her a good rest tonight,
and send your angels to protect him/her.
In the name of the Father, and of the + Son, and of the Holy Spirit
Or if you want a really simple one that isn't too fussy
May God bless + you, N
and keep you in love
Child answers AMEN!
Scripture to keep in mind
Six things there are, which the Lord hateth, and the seventh his soul detesteth:  Haughty eyes, a lying tongue, hands that shed innocent blood,  A heart that deviseth wicked plots, feet that are swift to run into mischief, A deceitful witness that uttereth lies, and him that soweth discord among brethren.  My son, keep the commandments of thy father, and forsake not the law of thy mother. ***Cf:Douay-Rheims Proverbs 6: 16-20
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