If you keep mom's food around, you will notice that the babies will eventually start being interested in it. 5 weeks is a good time. Some start earlier and some later. I mixed the dry food in with some wet food and fed 3 times a day, but the problem is that you waste a lot if they don't eat it all. So just pick up on their cues. Another thing - once they start eating food, momma will stop cleaning them up, so you have to provide a litter tray as well, and some supervision to make sure they know what to do.