I think one of the major factors in the size restriction is how disruptive the taller child might be and how polite the parents are about it. A friend brought her two children, one of which was too tall technically for Ketchakiddie, and asked a CM at the entrance to the area if it was okay if the taller one entered the water because they could not swim well and she was not comfortable sending her off alone at 7. The CM had no problem with it at all but just asked her to keep in mind to let the smaller children have pretty much the right of way. The two children were playing peacefully when my friend saw another tall child pushing little ones out of the way, splashing babies, etc., and the same CM kicked that family out of the area because they refused to keep the disruptive, tall child out of the water or make him behave.