Why Should A Child Be Careful To What They Say When Speaking To An Adult?

When I was younger ( I am 42 now) I was taught to be quiet and still while around grown-ups.  This approach is a bit over the top, but was not un-common.  In retrospect, as an adult, for a child to be courteous and respectful is very important  part of their social skills.  The adage of respecting your elders is very important and needs to be observed (even if the elders has not seemingly earned that respect).  With age comes experience and understanding.  I understand the importance of courtesy and respect now and can both show it,  and receive it, when dealing with others.  Many older people have suffered and sacrifice greatly, to provide securities now enjoyed by younger generations, and respect for that is due.   You did not elaborate as to what "careful" meant here.  Sometimes children when you least expect it will blurt out a truth, or something that may be taken out of the context of it actual meaning.  Children can be brutally honest, and thus upsetting an adults in certain social situations.  This is all very complex and is a part of our social relationships.  I personally believe that honesty and open communication is the best way to raise ones children.  I feel that a child or young person should feel free to ask any question and be given an honest answer to that question, even if its "I don't know".  The child or young person does need to realize that there is a time and place for things and that being impetuous (meaning acting with little or no thought towards others feelings) will cause discord in social settings.   I hope that this answered your question and will be of help to you!

P.s.  What I knew when I was younger is nothing compared to what I know today.  The experiences of my youth was only the first stones in my house of understanding.  That house is ever growing and taking on new additions all the time.  All built on the foundation of my earlier lessons from my parents.  Even though they were not all optimal, they each had a lesson, and had I listened more often I could have been saved from some of the pitfall I got myself into.  I think that a young person should listen and respect their elders but also keep in their minds and heart, their own unique ideas, with time and understanding melding them into one, to create a wonderful being,  YOU!

Bcuz its all about respect.
Youll want it to.

They might take it the wrong way and they dont care what kids have to say even though they say they do they really dont and the quicker kids learn that the better we will be