The kitten's poo will be softer and more frequent with 'wet food' as opposed to dry food,their poo will also smell worse and they will pass wind more frequently.This is not really a problem with cats fed solely on dry food.Have the kittens been wormed since you got them? this needs to be done regularly to keep them healthy.If you are worried about the kitten not cleaning itself then you may need to take it to the vet for a checkup,cats are usually very clean and not grooming themselves can be a sign of illness.