How to learn about children using hitting affectionately When I am about to leave, my youngest son will show affection by hugging me before I leave. When we are playing a game and he is really enjoying it, he will actually smile at me and hit me really quickly maybe 5 times a row. Sometimes this coincides snuggling his head into my body. 

Initially I thought he was being angry or acting out, it has become clear that he only does it a happy face while we are doing something fun. (And not in an "I am overwhelmed" kind of way. Lately I respond by returning a hug instead of giving him a surprised or irritated face, and he likes that).

Anyway, when I try to google to understand this, keywords such as "affectionate hitting" simply return thousands of "anti-parent hitting children sites". Is there an term for when children do this so I can find more helpful thoughts/discussion about this?
The search term "children hitting for fun" seems to yield the results you may want although the results seem to come from sites such as mumsnet.

An aspect to this phenomenon is that this behaviour may lead to bullying behaviour later on in life if the right responses are not given when this occurs.  The child needs to learn the cause and effect of hitting.

Typing the same term in Google Scholar gives research articles on dealing with bullying.