Although Krishna is known as Vaasudeva because He is the son of Vasudeva, the Azhvars praise Him as the son of Nandagopa, said M.A. Venkatakrishnan in a discourse. It is Krishna’s childhood leelas that are enjoyed by the Azhvars, and so, obviously, Nandagopa is the one who comes to mind. Vasudeva did not have the good fortune of seeing Krishna’s growing years. It is always a matter of joy to any child to be known as so and so’s son. Rama liked being called Dasaratha’s son. After the killing of Ravana, the devas praise Rama. Rama replies to them: Atmaanam maanusham manye raamam dasarathaathmajam (Yuddha Kanda). Here He says He thinks of Himself as a human being and as Rama the son of Dasaratha. Krishna too would have been delighted to have been called Vasudeva’s son or Nandagopa’s son. But since it was Nandagopa who was witness to Krishna’s amazing feats, naturally, “Nandagopan Kumaran” became the preferred way of referring to Him.
Kamsa, having come to know that Krishna is in Gokula, sees no reason to keep Vasudeva and Devaki imprisoned. So he releases them. Nandagopa goes to pay taxes to Kamsa, and while there, he meets his friend Vasudeva. Vasudeva enquires about Krishna, without revealing the truth about His parentage. But he mentions Balarama as his son, through Rohini. Balarama is also growing up in Gokula, and Vasudeva asks Nandagopa to take care of both Balarama and Krishna. Krishna, although He is in Gokula, is not entirely safe from Kamsa, who makes many attempts to kill the child. He sends demons like Cakatasura and the demoness Putana to kill Krishna, but these attempts fail. Many dangers are faced by Krishna when He is growing up as Nandagopa’s son, but He easily overcomes them all. Vanquishing His enemies is like child’s play to Him.