First, an angel was sent to Mary to tell her she was going to become pregnant by the power of the Holy Spirit. “The angel Gabriel was sent by God into a city of Galilee, named Nazareth, to a virgin…..named Mary…..He said, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS…..The Holy Spirit shall come upon thee, and the power of the Highest shalt overshadow thee: therefore also that holy thing which shalt be born of thee shall be called the Son of God.” Luke 1:26-35 (KJV)
Second, the Word (this was Jesus’s name before He became a human being) became a baby. “And the Word was made flesh, and dwelt among us, and we beheld his glory, the glory as of the only begotten of the Father…” John 1:14 (KJV).
The Apostle Paul further explained that “…although He existed in the form of God (as a spirit being)…(he) took upon him the form of a servant, and was made in the likeness of men: And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross.” Philippians 2:6-8 (NASB) The reason the Word was made the human being Jesus was so that He could redeem all mankind from sin and death through dying on the cross. “For since by man came death, by Man also came the resurrection of the dead. For as in Adam all die, even so in Christ all shall be made alive.” 1 Corinthians 15:21, 22 (NKJV) So, “How did Jesus come to earth?” If we go beyond these scriptures, we would only be speculating.
Additional Resource: This short, animated video is great especially for parents, children and Bible class teachers: Christian Questions CQ Kids Video “Why Did Jesus Come to Earth?”