I bought a size 5 for my my 17 months old baby and had to return this as it was small for him. His foot measured roughly 4.65 inches at the time. But I believe it's just Nike that doesn't have a standardized shoe sizing.
I bought 3 different pairs of Nikes, all of them size 5 including these sandals, a Jordan and a runner. The sandals were small, the Jordans fit and the runners were big. It would be helpful if Macys or Nike includes the length of each shoe, because apparently the size chart is not helping.