I watch several male celebrities kiss their sons on the lips is it ok? If so what age do you stop kissing your son on the lips?
I believe it is the INTENT behind the action that matters more than the action itself(as with ANY action IMO.)
If it's not done with a sexual intent...i don't see anything wrong with it...but culture can determine how you feel about a particular action for example:
In the U.S. hand-holding among older adults is consider sexual to some degree, and because of that you almost never see two men holding hands(unless you live in San Francisco like me), because we view it as 'something done on date, for a person you're interested in/attracted to etc.)'
In India(At least in Chennai, I understand not all of India has the same culture) Hand-holding isn't viewed as sexual, but rather a sign of friendship/partnership, it's VERY common to see two men holding hands as FRIENDS and nothing more.
So if the parent isn't getting some sort of sick-twisted thrill out of kissing their child on the lips....i don't see issues with it.