"Krsna's age is considered in three periods: from His appearance day to the end of His fifth year is called kaumara, from the beginning of the sixth year up to the end of the tenth year is called pauganda, and from the eleventh to the end of the fifteenth year is called kaisora. After the beginning of the sixteenth year, Krsna is called a yauvana, or a youth, and this continues with no change.
As far as Krsna's transcendental pastimes are concerned, they are mostly executed during the kaumara, pauganda and kaisora periods. His affectionate pastimes with His parents are executed during His kaumara age. His friendship with the cowherd boys is exhibited during the pauganda period. And His friendship with the gopis is exhibited during the age of kaisora. Krsna's pastimes at Vrndavana are finished by the end of His fifteenth year, and then He is transferred to Mathura and Dvaraka, where all other pastimes are performed."
Nectar of Devotion, Chapter 26
"One of them said, "My dear friends, considering His wonderful activities, how is it possible that such an uncommon boy would come and live with us in Vrndavana? It is really not possible. Just imagine! He is now only seven years old! How is it possible for Him to lift Govardhana Hill in one hand and hold it up just like the king of elephants holds a lotus flower? To lift a lotus flower is a most insignificant thing for an elephant, and similarly Krsna lifted Govardhana Hill without exertion. When He was simply a small baby and could not even see properly, He killed a great demon, Putana. While sucking her breast, He also sucked out her life-air. Krsna killed the Putana demon exactly as eternal time kills a living creature in due course. When He was only three months old, He was sleeping underneath a hand-driven cart. Being hungry for His mother's breast, He began to cry and throw His legs upwards. And from the kicking of His small feet the cart immediately broke apart and fell to pieces. When He was only one year old, He was carried away by the Trnavarta demon disguised as a whirlwind, and although He was taken very high in the sky, He simply hung on the neck of the demon and forced him to fall from the sky and immediately die. Once His mother, being disturbed by His stealing butter, tied Him to a wooden mortar, and the child pushed it towards a pair of trees known as yamala-arjuna and caused them to fall. Once, when He was engaged in tending the calves in the forest along with His elder brother, Balarama, a demon named Bakasura appeared, and Krsna at once bifurcated the demon's beak. When the demon known as Vatsasura entered among the calves tended by Krsna with a desire to kill Him, He immediately detected the demon, killed him, and threw him into a tree. When Krsna, along with His brother, Balarama, entered the Talavana forest, the demon known as Dhenukasura, in the shape of an ass, attacked Them and was immediately killed by Balarama, who caught his hind legs and threw him in a palm tree. Although the Dhenukasura demon was assisted by his cohorts, also in the shape of asses, all were killed, and the Talavana forest was then open for the use of the animals and inhabitants of Vrndavana. When Pralambasura entered amongst His cowherd boyfriends, He caused his death by Balarama. Thereafter, Krsna saved His friends and cows from the severe forest fire, and He chastised the Kaliya serpent in the lake of the Yamuna and forced him to leave the vicinity of the Yamuna River; He thereby made the water of the Yamuna poisonless."
Krsna Book, Chapter 26
Bhaktivedanta Book Trust. Excerpted from texts and purports of HDG A.C. Bhaktivedanta Swami Srila Prabhupada.