The lyrics are pretty heavy; sounds like young lovers took a relationship to the physical consummation and ended up conceiving. They weren't prepared for a life-changing event of that magnitude, yet they knew beforehand that a baby was a potential consequence of their decision (hence the song title). They had to grow up fast, but ended up seeing the wondrous side of creating a new life, and that sometimes even our mistakes can work out for good.
Or at least that's how I'm interpreting it... what do you think?
"Riding on the fumes that spark us
while igniting dreams..."