Ryan has had a rash over a majority of his body since last night. It is worse today and is raised in some areas. It also got really itchy right before bed and he was miserable and crying because it was bothering him so much. His temperature has also been up slightly, but is not considered too high at this point. This all could be a sign that he is in the process of engrafting, which should be anytime now.
However, it could also be the start of something bad like Engraftment Syndrome (ES) which has not been studied much in pediatric populations, but is generally associated with a higher rate of graft rejection and a higher mortality rate.
It could also be early Graft Versus Host Disease (GVHD). Ryan is the "host" and the "graft" is the donor marrow. In GVHD, the graft attacks the host, which can result in problems that range from minor skin issues to major organ failure.
I am going to assume it is just his body working to engraft the marrow. But I will definitely have some questions for the team during rounds in the morning.