Do you mean food meant for baby people? Is the "false b vit" maybe "synthetic"?
If it's food meant for people of any age, and you intend to feed it to the chickens for just a day or so until you can buy more proper chicken feed, then it's probably fine. Synthetic vitamins are probably just fine, as long as it's not a ridiculously high dose, and as long as you're feeding it short term. Long term, it's probably safe at some levels and not at others, but I have not idea what levels are Ok and what ones are not.
It looks like you already know proper chicken feed is the easiest way to give them a proper balanced diet, so I assume you'll be buying more really soon