Beginning at about four months, sensory and motor integration begin. At about 10-12 months the limbic system, which is deep in the brain and controls emotion, starts. This is why 4 month olds are not capable of having………but 10-12 months and 15 months old can have great ones. They are just starting to develop that emotional part of the brain, and in fact before it is fully developed they can’t even control their emotions very very well.