How small is too small for food

So I recently got a ball python, and my parents unknowingly got a pack of fuzzy mice for feeding, but these are half of the recommended size (thickness of the snake). Can I still feed these or are they too small for feeding?

Yes, you can still feed them, but you might want to try feeding 2 per feeding, as one is a very small meal even for a hatchling BP. FYI, some snakes (especially BPs) can be funny about taking 2 items per meal (they only want one regardless of size), but no harm trying. If yours just won't, well then you'll know.

As you probably know, most young BPs are taking "hopper" mice.