Polly spends her day discovering the world by putting almost everything she touches in her mouth. this implies that she is in piaget's first cognitive stage known as the

The answer to this question is sensorimotor
According to Piaget, during the sensorimotor stage, Children will try to find the correlation between their body and the environment.
Because of this, they will try to instinctively put every object around them inside their body and will continue to do so for about 24 months.