It has become a widely accepted custom for the father to bless his children on the eve of the Day of Atonement. The placing of both hands upon the child's head when conferring the blessing, symbolizes that the blessing is bestowed with fullness of spirit and heart.
According to the Chayyei Odom, the proper text of the blessing is as follows:
For a son:
יְשִׂימְךָ אֱלֹהִים כְּאֶפְרַיִם וְכִמְנַשֶּׁה, יְבָרֶכְךָ יְהֹוָה וְיִשְׁמְרֶךָ: יָאֵר יְהֹוָה פָּנָיו אֵלֶיךָ וִיחֻנֶּךָּ: יִשָּׂא יְהֹוָה פָּנָיו אֵלֶיךָ וְיָשֵׂם לְךָ שָׁלוֹם: May God make you like Ephraim and Menashe. May Adonoy bless you and guard you. May Adonoy shine His countenance upon you, and be gracious unto you. May Adonoy turn His countenance toward you and grant you peace.
Continue “And may it be the will” below
For a daughter:
יְשִׂימֵךְ אֱלֹהִים כְּשָׂרָה רִבְקָה רָחֵל וְלֵאָה. יְבָרֶכְךָ יְהֹוָה וְיִשְׁמְרֶךָ: יָאֵר יְהֹוָה פָּנָיו אֵלֶיךָ וִיחֻנֶּךָּ: יִשָּׂא יְהֹוָה פָּנָיו אֵלֶיךָ וְיָשֵׂם לְךָ שָׁלוֹם: May God make you like Sarah, Rivkah, Rachel and Leah. May Adonoy bless you and guard you. May Adonoy shine His countenance upon you, and be gracious unto you. May Adonoy turn His countenance toward you and grant you peace.
(Continue:)
וִיהִי רָצוֹן מִלִּפְנֵי אָבִינוּ שֶׁבַּשָּׁמַיִם, שֶׁיִּתֵּן בְּלִבְּךָ אַהֲבָתוֹ וְיִרְאָתוֹ וְתִהְיֶה יִרְאַת יְהֹוָה עַל פָּנֶיךָ כָּל יָמֶיךָ שֶׁלֹּא תֶחֱטָא, וּתְהִי חֶשְׁקְךָ בַּתּוֹרָה וּבְמִצְוֹת עֵינֶיךָ לְנֹכַח יַבִּיטוּ פִּיךָ יְדַבֵּר חָכְמוֹת וְלִבְּךָ יֶהְגֶּה אֵימוֹת: יָדֶיךָ יַעַסְקוּ בְּמִצְוֹת. רַגְלֶיךָ יָרוּצוּ לַעֲשׂוֹת רְצוֹן אָבִיךָ שֶׁבַּשָּׁמַיִם. יִתֵּן לְךָ בָּנִים וּבָנוֹת צַדִּיקִים וְצִדְקָנִיּוֹת עוֹסְקִים בַּתּוֹרָה וּבְמִצְוֹת כָּל יְמֵיהֶם, וִיהִי מְקוֹרְךָ בָּרוּךְ. וְיַזְמִין לְךָ פַּרְנָסָתְךָ בְּהֶתֵּר בְּנַחַת וּבְרֶוַח מִתַּחַת יָדוֹ הָרְחָבָה וְלֹא עַל יְדֵי מַתְּנַת בָּשָׂר וָדָם פַּרְנָסָה שֶׁתִּהְיֶה פָּנוּי לַעֲבוֹדַת יְהֹוָה וְתִכָּתֵב וְתֵחָתֵם לְחַיִּים טוֹבִים וַאֲרֻכִים בְּתוֹךְ כָּל צַדִּיקֵי יִשְׂרָאֵל אָמֵן: And may it be the will of our Father in heaven, to place in your heart love and fear of Him. May the fear of Adonoy be upon your face all the days of your life, so that you will not sin. May your desire be for Torah and Mitzvos, may your eyes look straightforward, may your mouth speak [with] wisdom, may your heart meditate [with] reverence, may your hands be engaged in mitzvos, and may your feet hasten to do the will of our Father in heaven. May the Almighty grant you children who will [grow up to] be righteous, occupying themselves with Torah and mitzvos all their days. May your source be blessed, and may He grant that your livelihood come with honesty, ease and abundance, from His generous hand, and not from the gifts of men; a livelihood that will free you to serve God. May you be inscribed and sealed for good, long life together with all the righteous of Yisrael. Amein.