Along came/comes xxx = xxxx arrived/arrives.
You can say "xxxx came along", but it is not as rhythmic in a song, and could have another meaning that xxx accompanied us.
The phrase can be used with anything:
"Along came the herd of horses, galloping past"
"Oh, look, there's Dickie! Along comes trouble!"
"As we drove up the motorway, along came the police car."
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