Sucking the tongue of your grandchild to relieve him

In answer to the video "Muhammad did it. Therefore it is not sinful."

Not every saying and action of the prophet is meant to be emulated. One doesnt need, in all cases, to apply saliva or suck on a child's tongue to relieve him from thirst as the prophet and desert Arabs did when in the absence of water in the extreme conditions of their environment. 

"The Messenger of Allah, peace and blessings be upon him, heard Hasan and Hussein crying while they were with their mother, so he hurried to them and he said: What is the matter with my boys? Their mother said: It is thirst". As the water source had dried out, the Prophet called out: "Does anyone have any water?" As nobody answered, he asked for one of his grandchildren be brought to him "He massaged his tongue and moistened it until he calmed down".

This obviously is a practical solution to a specific situation. We arent talking here of rubbing adult tongues and ears with one's saliva as some are depicted in the NT Mk7:33,Jn9:6.