At what stage is it easiest to train a child

Giving birth to a child is every mothers dream and every fathers pride but to bring up a child isn't the easiest thing it takes a lot of patience,endurance,courage,determination and love kudos to those who have done well and to those who aren't doing such a great job you could always use a bit of moral support every now and then

At what stage of maturity is it easiest to train a child,every stage in a child's life has its ups and downs but which stage do u think is the easiest stage in a child's life to train them