It appears to be one post on a forum that the Daily Mail has picked up on. Good job they don't read AB.
This is not Government advice to parents, and is probably just an individuals opinion, though they might be representing an organisation (but the DM doesn't tell us which).
The sex education forum appears to be a voluntary members organisation set up to aid practitioners. Membership is open and its opinions and guidance is not mandatory or binding on anyone.
http://www.sexeducationforum.org.uk/about-us.aspx
Most children will happily and voluntarily kiss their grand parents. If the child for some reason, doesn't want to, are we really saying that child should be forced to? I definitely agree with the 'miss', forcing a child to kiss at adult is very wrong.