I have a question about vietnamese culture.

Question

How is touching a kid's head insulting?

Answer 1

We believe that the head is the highest and most sacred because that's where our God, ancestor "live".  Our tradition is very similar with the Thai people too.  But as an adult you can touch the child's head without insulting.  It is insulting when you are younger and touch the head of someone older than you.  

Answer 2

It's a Buddhist thing.

The head is the highest part of the body and contains the most important organ...the brain. It is jealously guarded...and for good reason obviously.

The foot is the lowest organ and the dirtiest, so never point your foot at someone unless you want to insult them.

When in doubt, don't touch.