I think it determines the age. As babies and toddlers it was always kisses everywhere on the face because they are adorable. But even as they grew we always kiss on the lips. But there's a time in a kids life when he goes from calling you daddy to dad. The same goes for kissing on the lips..one day it will change from kiss on lips to kiss on cheek. It just changes as kids get older and their comfortability with kissing changes.

There is nothing wrong with kissing your son. I kiss my baby all the time with peck
Now if its a different kind of kiss than a peck than depending on your culture it may be acceptable. People need to realize other cultures show there affection differently than you may so u should not judge

You stop when your son tell you to stop

Hi, I don't see a problem, take your queue from your child, if your child wants to then fine, my daughter is a loving and affectionate child and if I had a boy, my view would not change, hugs and kisses are so important to their development and confidence, too much talk of the bad things today, remember good family values and live by them, all the best, Ferry.