DS does that sometimes and I usually gently remove his hand, tell him Ow that hurts mama, and hand him his burp cloth to hold. If he gets really persistent and doesn't stop, I will unlatch him for a few moments and tell him No pinching, that hurts. Sometimes it works and sometimes it doesn't LOL. Good luck, mama, I feel your pain.
Faith - WOHM to DD born 10/2006 DS born 8/2011 :