Mary Ainsworth developed the Attachment Theory. As a product of her '"Strange Situation Procedure" study, she concluded that there are 3 types of attachment: Secure, Resistant, and Avoidant.
In the case exposed in the question, Kyle has developed a secure attachment. In this type of attachment, a kid uses her mother as a base where he is safe and will let him explore his environment. According to Ainsworth's study, this type of attachment is present in close to 70% of infants.