Since yesterday when one of my 5 week old kittens died I have done nothing but watch them to ensure they are ok 
I have had other litters before both sets survived and were very healthy and boisterous .
The 3 remaining ones I have seem terribly small for their age (6 weeks on Tuesday) I have tried introducing them to food but they only sit in it & its the same with water 
They only opened their eyes 12 days ago which I know is late & they sleep for about 90% of the day .
I'm just at a loss as losing the kitten has completely thrown me and I can't remember what I'm supposed to do

Can anybody advise me ?