CRA is quite clear that you can only claim donations and gifts made by you or your spouse or common law partner on your return. Please see http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns300-350/349/menu-eng.html
You should also note that your son can carry forward this donation for the next 5 years.
Perhaps one reason why CRA does not permit transferring donations to other family members is where would you draw the line... ie) my 30 year old child or my mother does not need all their donations or, it is more beneficial for me to claim all the donations made by my family members on my return.
Maybe you can contact the charitable organization and ask if they can reissue the receipt in your name.
