On a more human level, the heavenly voice assures Jesus that, when all his brothers desert him and when his mother has been entrusted into the care of John and when all hell is breaking loose upon him, nevertheless he is still a child. He is always a child, the child of his heavenly Father.
This is something that Jesus will hold on to even in the darkest hours. In Gethsemane, he will pray, “Abba, my Father.” And at the end, he will say, “Father, into your hands I commit my spirit." Jesus is forever the child of God.