The first thing to know and to remember about giving and getting blessings is that the source of all blessing is G-d alone.
In reward for cleaving to Him, G-d blessed Abraham "I will make you a great nation [with children], and I will bless you [with wealth] and make your name great [with honor], and you will be a blessing" (Gen. 12:2, Rashi). Not only is Abraham promised to bear G-d’s blessing, but also to pass it on to others: "and in you shall all the families of the earth be blessed" (Gen. 12:3).
G-d said, until now I alone decided who would be blessed, now you may also decide who I shall bless (Rashi).
Abraham’s power to bless others was transmitted to his children. Isaac blessed Jacob. (Gen. 27:4). Jacob later transferred this blessing to his twelve sons, "every one according to his blessing he blessed them" (Gen. 49:28) as well as to the two sons of Joseph: Ephraim and Menashe. G-d bestowed blessing upon the High Priest Aaron and his descendants, and commanded them to perpetually bless the Jewish people (Num. 6:22-27).
We too should perpetuate this tradition by blessing our children every Friday night. It is a moment filled with love and meaning.
How to Bless?
There are different customs. Some people bless their children before kiddush and some after kiddush (this is the Sephardic custom). Some go to their children, others have the children come to them. In some homes the father gives the blessing to each child; in others it is both parents. Among Sepharadim it was customary for the child to kiss the parent’s hand as a sign of honor and respect before receiving a blessing.
The parent’s right hand, or sometimes two hands, are placed on the child's head and the introduction is altered depending on whether the child being blessed is a boy or girl followed by the words of the blessing from the BirkatKohanim (Bemidbar 6:24-26) as follows:
For boys, the introductory line is:
May you be like Ephraim and Menashe.
יְשִׂימְךָ אלקים כְּאֶפְרַיְם וְכִמְנַשֶּׁה.
For girls, the introductory line is:
May you be like Sarah, Rebecca, Rachel, and Leah.
יְשִׂימֵךְ אלקים כְּשָׂרָה רִבְקָה רָחֵל וְלֵאָה.
For both boys and girls, the rest of the blessing is:
May G-d bless you and guard you.
יְבָרֶכְךָ ה’ וְיִשְׁמְרֶךָ
May G-d show you favor and be gracious to you.
יָאֵר ה’ פָּנָיו אֵלֶיךָ וִיחֻנֶּךָּ
May G-d show you kindness and grant you peace.
יִשָּׂא ה’ פָּנָיו אֵלֶיךָ וְיָשֵׂם לְךָ שָׁלום
Afterward, it's nice to whisper something personal into the child's ear, praising some accomplishment in his or her week, such as a good mark on a test or playing nicely with a kid brother. It's your special moment with your child – use it as a way of connecting in your own personal way.