The way I interpret it, Chihiro’s parents wouldn’t ordinarily act like that and did so only because the food (which we later know to be cursed) existed specifically to be a trap, and so had some magical lure on it that made it even more seductive and impossible to resist - like how siren song draws sailors to their deaths, even against their better judgement.

Indeed, her parents acting out of character is at least part of why Chihiro is uncomfortable with the situation.