When I was a child, my parents would bless my siblings and me on Erev Shabbos. The formulation that they used was "Yesimcha Elokim kEphraim v'ch'Menashe" for each son and "Yesimech Elokim kSarah, Rivka, Rachel, V'Leah" for each daughter, and then they would say the kohen's blessing "yevarechicha..." once for everyone together.
Usually when I have seen other families blessing their children, they do it quietly so it is difficult for others to hear, but I believe that they say the kohen blessing separately for each child. Is this the typical practice?
:-)
In any event, no, no source now. Sorry.