My 4 months old Border Collie try to bite my face TOO OFTEN..

I was in my bed 5 minutes ago and I just reached to pet him he was playing with is toy and when he saw I can't reach him, he gets up and sit next to my bed for me to pet his head... but when he seems calm and relax without even looking me he jump for my nose! He doesn't seem like his playing and after that he know he did something wrong! He has already done that a few weeks back and I still have teeths marks on my nose.. yesterday he did it on my arm! He's not agressive except for that I want to find a solution fast.. my brother have a daughter and a son of 4 years old and 4 months old and I will NOT tolerate my dog bitting them because he wants to!... please help I don't know what do to..