What happens when it is time to start school? Most school districts have rules about how old you have to be in order to start school. I believe for many that the cutoff is December 31st. You have to have your fifth birthday before December 31st in order to start the first grade the previous September.
Waiver? Hold the first kid back a year? I'd say the parents are going to want to have that discussion with the school district well in advance.