User blog comment:EmpyreanSmoke/Supernatural Q&A/@comment-79.115.73.90-20150816170909/@comment-24834479-20150819002105

If there are any more special kids left, then they will be dealing with their "gifts", no longer apart of Yellow Eye's plan.

The demon blood has to enter their body at a very young age so that it can develope their powers as they grow, which is why Sam received his visions in his 20's. It is possible that angel blood could have a magical affect on humans, but angel grace isn't compatible with their souls.