Kissing ones Mother when a Niddah

Is it permitted for a boy over Bar Mitvah to Kiss and Hug his Mother even when she is a Niddah? If the answer is Yes, then why should this be allowed, seeing that the Issur of Niddah applies even to an unmarried single girl? If it is in deed not allowed, then does a child need to be informed as to when his Mother is ok and when she is off-limits?

Shalom U'verachah, Parents are allowed to kiss their children even over bar and bat mitzvah as this has no sexual overtones and as we are today not particular about tumah and taharah this is permitted. There are certain communities where such contact is frowned upon and one should act as is appropriate for the community where he lives. Kol Tuv