Answer:
Sensorimotor stage of development
Explanation:
Piaget's theory of cognitive development has four stages of development and sensorimotor is the first stage of child development. At sensorimotor stage the child learns by assimilation and accommodation, he/she tries to know the environment by using the senses. This period lasts for the first two years of the child's birth.
Damien puts those things in the mouth just to have a feel of them by sucking them. When he sees the toy train he plays with it but when he did not sense it he loses interest. Damien behaviour illustrates a child in the sensorimotor stage of development.