Young mother cat is not taking proper care of kitten, is this normal?

I have been taking care of a stray cat the past year, I would say she is about a year and a few months old, we were just going to take her to get fixed after this past winter, but she ended up getting pregnant. She had 3 kittens one week ago and the 2 bigger kittens died at birth, leaving 1 small kitten to survive. The first day she was very disorineted + the kitten was so small we took her 2 the vet 2 hours after birth, the vet did x-rays, etc- claimed everything was fine with both. That night and the following 2 days she was attentive to the kitten and her natural instincts took over and we thought she would do her job as the mother cats do. The past 3-4 days though the mother cat has been "childish" by leaving the baby and not paying any attention to it, wanting our full attention and wanting to play. We try to place the kitten by her stomach and help it find a nipple to eat and when he finds the mother will push him away. And today we found the kitten out of his box in the dirty