Those mushrooms have faces, were they once living creatures or are they just faced mushrooms?
The story of the original Super Mario Brothers said that Bowser had transformed the citizens of the Mushroom Kingdom into (amongst other things) mushrooms. The mushrooms in Super Mario Brothers have faces because they are transformed human citizens of the kingdom.
According to the official story, these citizens were also transformed into blocks, and other unnamed things. Fire flowers aren't explicitly mentioned in the story, but we can probably safely assume that they're included in the list of things that citizens were transformed into.
So yeah, when Mario's eating mushrooms, those were previously human citizens of the Mushroom Kingdom. When he's destroying blocks, those were also once citizens of the Mushroom Kingdom. Since Toads and Goombas both look like blends between humans and mushrooms (with toads closer to being humans and goombas appearing to be closer to mushrooms), it's probably safe to say that both those groups were also human citizens, before the coming of Bowser.
This is as distinct from the Koopa Troopas, who are pretty clearly more closely affiliated with Bowser, and probably are not transformed citizens.
Incidentally, the reason originally given for Bowser always kidnapping the princess is that for some unexplained reason, she's the only one who can undo the curse and return everyone to their normal forms. One can only wonder why she apparently didn't do so, after being rescued.