If they are nursing from mom and are content and not crying or acting hungry, they probably won't show much interest in solid foods till 6 weeks. Sometimes you might get one or two interested at 5 weeks, but its a lot less frustration to wait another 2 weeks to attempt to start them on solid foods.
When you do, I find the best thing is canned kitten food that is made soupy with warm water and a little KMR and you kinda put some on your fingers and put it in their mouth to get used to the taste. Once they do, feed them on a shallow plate and on a washable surface. You might have to kinda push their mouth/chin in a few times before they start tasting it.