When I went back to pick up Suzi and Peter the neurosurgeon came back in and said that since Peter had a runny nose they wanted to keep him there for another twelve hours for observation. Apparently something that is fairly common with head injuries is that the spinal fluid will leak out the nose or ears. Since the fluid can get out, bacteria can get in. If that happened Peter would develop Spinal Meningitis, a fairly serious and painful illness.
But, with the blessings of the faith and a whole bunch of prayer we were not able to collect enough of it for them to test and they eventually said it must have been just a runny nose since it was not consistent at all.
Peter is excited to be home, although he is restricted from doing most the stuff a four year old does, he has most of his freedoms back and does not have to stay in bed all day hooked up to machines.