poor baby!!!!! the exact same thing happened to both myself and my brother when we were little. with me, i was six running around playing hide and seek and we were slamming doors and somehow my finger got slammed and my whole nail on my middle finger fell off. and w/ my brother it was exactly like your son, he was so little about one i think and was playing by the bathroom door and my uncle didn't notice and closed the door and my brother's finger was caught in between the door and hinges the entire time my uncle was in the bathroom and he didn't cry until my uncle came out. i still wince thinking about my poor little brother.
anyway sorry for the tangent, i will definitely say a prayer for your son!! keep us updated ok?