I have bottle fed plenty of kittens and the round the clock chore isn't fun! It would be ideal for the kittens to have their mother to nurse off of. She is no doubt looking for them. Left unspayed she's apt to have at least two more litters before the year is up, and that makes for one calcium depleted cat. Not to mention more kittens that will either grow up wild, or be found by someone else. PLEASE try and find the mom cat and get her spayed at the very least.