C.G.
Well like you I think this is just adorable...but on the other hand when my daughter was in kindergarten a little boy stuck his hand down her pants...not so adorable! So I guess it comes down to teaching boundaries. I think perhaps you might teach him that way. Maybe the personal space thing. You could say something like "Mommy and Daddy and Grandma and Grandpa love your kisses but sometimes people don't want to be kissed". Maybe teach him to reserve his kisses for family members, at least until he's old enough to understand.
I would hate for your little guy to get into something serious over is innocent affection for others.
It's a sad world we live in but it is indeed the world we live in...