It depends on the extent of the internal injury, probably located to the urinary system. It should be seen by a doctor.
The first thing you need to do is to take it to a vet. There are many causes of diarrhoea, and some are potentially fatal. It's better to have the kitten treated properly. In the meantime, avoid giving it any milk or wet food products.
If it is cow's milk, it could make the kitten sick. Some cats are lactose intolerant and such a young kitten getting diarrhoea can quickly leave it severely dehydrated with can become fatal in a matter of days. Specially formulated kitten milk that are found in most stores are perfectly safe for kittens and adults to drink as a treat.
I have a 5 week old kitten that my fiancée and I rescued and he's healthy at 1.3lbs
there are spacial kitten foods.
A 4 week old kitten's eyes are not supposed not to be small since they open up by the second week hence they are becoming big.
it is very fatal, if not treated quickly you may die within a week
if your kitten is bleeding from his "bum" he is sick and should go to a vet
take it to the vet
Kidney stones
from its moms milk it
no they need kmr or kitten formula ring a vet for advice on feeding
You cannot keep a kitten in a cage for any long period of time.