How do they do it?

I want to know how momma cats do it. If you've ever watched kittens nurse you know how they knead at their momma as they eat. Don't they have claws at that point? Cause all I have to say is ouch! Benjamin will be 6 months on Sunday and he has started to grab, knead and pinch as he feeds. I cut his nails but that didn't help. He has the grabbing method worked out pretty well. I fully sympathize with all mother cats out there.