Around the age of six months babies begin to sit on their own, allowing them to free up their hands for exploring.  Before you know it they are reaching and grasping.  Once movements become more purposeful they discover cause and effect.  Toys such as this pop up pictured, give children a chance to learn how objects work and help make the cognitive connections between their actions and consequences.  Children also gain a better sense of self-awareness and control over their environment.  Musical instruments are also a great way to introduce cause and effect.