why the children must send there parents to an instition?

Answer 1

If you mean a nursing home, most adult children would do this because they are unable to provide 24 hour care. My father in law recently moved in with us. He is 82. Right now we can leave him alone during the day when we go to work. If it gets to the point where he requires 24 hour care we would have to bring in a nurse so that we can work. I also would not be able to bathe him, etc. so we would need help with that.
We will keep him at home as long as we can. If it reaches that point that he must enter an insitution we will do that because it will be in his best interest. He deserves specialized care.
I think that some people do it because they do not have room for the parents in their home. They may also do it because they want their elderly parents to be able to socialize and the nursing homes offer outings and get togethers. The elderly do not feel as lonely. They get to do projects, play games and have company. Sometimes they even find boyfriends or girlfriends and this is wonderful company for them.

Answer 2

Did you mean "institution" as in a place for the mentally ill? If so, adult children would send a parent there because it was the best treatment for their mental disease. Minor children wouldn't send their parents anywhere since the parents would be the one having the authority over their minor children.