My little brother keeps kicking me in the nuts?

My bro is ten and a nice person hes not usually bad, im 15 and last week he kikcked me in the nuts not knowing how much it hurts, i was in pain and he was laughing i tol him not to do it again and he has done it 3 times since, I want to kick him back to show him how much it hurts but i feel like i shouldnt because hes my brother. What shall i do to stop him kikcking my nuts?