Feeding her kittens

On the third day after the bath the mother lay down outside her new house and fed her kittens. This was a breakthrough. And she did not leave this day, at all.
On the fourth day she washed her kittens a little, and she fed them regularly. She washed herself. She yelled at me for coming too close but then she saw the Swedish cat food on the plate and the yelling turned to this rolling throaty R-sound, the message for her kittens to come eat.
On the fifth day after the bath the lice were mostly dead. The kittens' eyes didn't crust over as badly anymore but they still need very regular cleaning because there is still a bit of puss. I went to the vet and bought antibiotics that I will feed the kittens twice daily until their eyes have cleared completely.
The kittens spent the sixth day playing, drinking from their mom, eating Swedish cat food, and they are learning how to pee in a litterbox I placed next to their new home. They also cleaned themselves a little. And their mother licked both of them quite frequently.
I am going to the vet this morning to buy substitute mother's milk that I will place next to the regular food.

The little family enjoying life in the sun

P.S. I did buy substitute mother's milk but the kittens won't touch it. Why?