The arguments for starting children in school later hold no water. Spending more time at school than with family prepares children for the reality of working life. The parents need to spend more time at work than with family, so there's no point in holding the children out of school for family life reasons. Children become better socialized to the corporate social structure and disciplined into a hierarchy better the sooner they start school. Acclimating them to this sort of social structure prepares them for working life sooner. The sooner children start school, the sooner they can start learning skills that make them useful in the workforce.
Having the children in school earlier is also good for the parents. With the children at home instead of school means that the parents can't be at work. This is a serious drain on productivity. The sooner we get children into schools, the sooner we get the parents back to full time productive work.