If you can’t give them a full meal, start with 1/4 of the food (or whatever amount they’ll accept) and offer it frequently. Make sure their water bowl is always filled to the brim, and that they always have fresh water available. As time goes on, try feeding them less frequently — maybe once or twice a day instead of 4 times!
Also remember: The more often you feed your cat’s normal food at first, the better he will adjust after weaning off the milk replacer. And please don’t feel too bad if your kitten doesn’t get used to this sooner than later! If he won’t eat his regular food right away — take heart in knowing that many cats do not like change until they’re older than 2 months old. Be patient and work with him as much as possible before considering other measures such as switching foods or changing brands completely. You might want to go ahead and mix some kibble into his milk replacement just for fun things while you wait for him to become accustomed to solid foods again!