Do you think that children need to be sheltered from unhappiness? (explain why or why not.)

I think personally, you tell them gradually, as things happen you explain to them.

for example if grandma dies, you explain that everyone will die, but not to be scared because it's natural, and it's a far while away for them.

but you don't just tell them that the world is as harsh place and to have no expectations in life cause it's all going to end one day.

you have to nurture their curiousity, without exposing things that are beyond their years.

so don't shelter them, but at the same time, don't just tell them the world is black and white, and shove it in their face all at once.

try to let them learn on their own, whilst explaining.

show them the beauty in things!

I firmly believe that attempting to hide reality from children is one of the worst mistakes a person can make; allow a child to live a life free from harm, sadness, or any emotion besides pure and utter happiness... Of course, a child's youth should be cherished and given all the opportunities that get's given to them, but it is singlehandedly the worst way to prepare a child for the future, and for fate! 
Imagine this: your child is eleven, and is getting picked on by some bullies. They are calling him names and he is cowering under them, silently pleading for his mother to come and stop them; not allowing for him to stand up for himself. Of course, the mother comes rushing in and shoo's the bullies away, and allows the child to be enveloped in her love, free from harm. Indeed, it is good that the child is no longer in a harsh environment, but the fact that the child has no social skills, no confidence and no initiative to stand up for himself, is a huge worry, since in the real world, life isn't always fun and games; things happen, people aren't always nice. Having the courage and initiative to stand up for themselves - feeling sadness in the process - allows them to grow as individuals.
They say that it's better when a child falls over and scrapes their knee, to get up on their own before their mother comes and runs to them! This allows them to get up on their own and prepares them for the future.
Kids nowadays are wrapped up in cotton wool; the love that mothers and fathers have for their children wants for their children to sidestep any harm or unhappiness, for they think that their children are far too delicate to be sad. It is crucial for our generation to stop wrapping our children in cotton wool; to let fate happen and allow for them to get up on their own when they scrape their knee. Happiness is temporary, as is unhappiness... Learning to embrace and experience both of these emotions as children need to be prepared for the future; to be strong, independent adults with more initiative than ever. So all in all no, children should definitely not be sheltered from unhappiness.