thank you for your query.... well according to the problem, fathers blood group A+ mothers blood group AB+ their childrens blood group A+ now as for blood donation, groups A+ can donate to A+ & AB+ groups B+ can donate to B+ & AB+ groups AB+ can donate to AB+ groups O+ can donate to all positive blood groups now Rh factor is the +/- sign that you see with the blood group.. Rh + patients can safely take blood from + patients only whereas Rh - patients can give blood to both + and - patients... thus group O- becomes universal donor....i.e. persons having O- blood group can donate blood to any group.... and similarly group AB is called as universal receiver..... hope that clears the confusion.... as per the question is concerned, the son A+ can definitely donate blood to mother AB+ when all the other parameters are matched and compatible...i.e. no infections, son is physically able to donate blood etc.... you can contact me for further questions... i will be happy to help... regards