I think he singing about being in a band is not as great as it seems. When he says "just kids pretending to be astronauts, police officers, and firemen" He means little kids want to grow up to be firemen, police officers, and astronaut's, but usually those dreams never happen. Maybe his dream was to grow up to be in a band, and it happened, but it's much harder than he thought, so the joke is on him.
I think he singing about being in a band is not as great as it seems. When he says "just kids pretending to be astronauts, police officers, and firemen" He means little kids want to grow up to be firemen, police officers, and astronaut's, but usually those dreams never happen. Maybe his dream was to grow up to be in a band, and it happened, but it's much harder than he thought, so the joke is on him.