The Clinton Foundation was a terrible conflict of interest. It wasn't a big secret that government officials had to donate to the Clinton Foundation in order to get an audience with Clinton. Trump has decided not to play that game. For that reason, it's important that his son shuts down his charity.
The president-elect's son was right to shut down is charity. The president-elect does not want any potential conflicts of interest to arise during his presidency. Therefore, it is good to close the charity, and to sell off any business interest that might cause trouble for his administration down the road.
Trump's son should not shut down his charity. In fact he should focus on that and not his father's political career. Trump's son is grown and with a life of his own. Especially now that his father has accomplished his goal of reaching the white house, his son should go back to his own life. He should continue to do good work through his charity and remove himself from his father's career instead.
If it is his son's charity, then his son should be allowed to do whatever he wants with it. I don't know how this would pose a conflict of interest for the President. Apparently it has something to do with his sister participating in both the charity and her father's presidency.