In John's Gospel the miracles are presented as seven "signs" - pointers to who Jesus really is. We're supposed to see the signs through John's testimony, and believe in Jesus as the Son of God (John 20:31)
That's a really helpful perspective in Sunday School, because the children might be wondering why Christians can't do miracles like Jesus' today. The obviuous answer is: because we're not the Son of God! At the same time, it's vital that John gives us the evidence that Jesus IS the Son of God - otherwise, how would we know to believe?
The song "Seven Signs" takes us through the signs as they come up, and asks what they're all about - with the great answer: they're about Jesus being the Son of God!