I am going through the same thing with my 4 1/2 week old babies. I started to introduce kitten food to them on their 4th week birthday (Tuesday just past). 1st day, no interest whatsover. Just wanted momma. 2nd day, a little interest from one kitten. 3rd day, same kitten and now another one are eating the solid food. HOWEVER, my problem is momma. She devours every piece of food around her, and I have to keep her out of the room when the food is down for the babies. She will not let them have even a nibble. It's a little tiring, especially since I work all day, so the only time I get to show them how to eat is in the morning and when I get home after work. And by that time, all they want to do is play.
Same thing with the litter, right now it's a bed and food to munch on. Not a potty. Although, my DH said he saw one of them squatting and having a pee in it the other day, but I don't know for sure.
I really thought it was going to be easier than this.