In addition to Vladimirs answer I'd like to add that sucking on their mother and siblings is natural behavior for kittens and works literally like a pacifier. It helps them form social connections with their siblings and mother, calms them and makes them feel protected. 

I totally understand not wanting to be pawed at with needle-sharp claws, but depriving the kittens of their sucking behavior can lead to abnormal social behavior. We've once had a cat that was taken from his mother too early and he developed some obsessive sucking behavior every time someone lied down on the couch with a blanked. He absolutely soaked the blanked with saliva and didn't stop this infantile behavior even when he became an adult.

So I suggest you let them suck at you, but protect your skin from their claws and teeth with some clean cotton fabric. Maybe you have something like old cloth napkins, baby swaddling cloths or dish towels lying around that are easy to wash and can take some abuse. Have a few of them arms length wherever you usually interact with the kittens and wash them regularly.