As his eight-year-old son blew out the candles on his birthday cake in February, Choi Nam-joon gave him a present he hopes will keep growing long after the party ends: three shares of Samsung Electronics.The shares, worth a total of about 500,000 won (US$332) at the time, were added to the boy’s brokerage account, part of a plan the 42-year-old South Korean office worker sees as the most realistic way to help his son build wealth.Choi’s family cannot afford to buy a home in one of Seoul’s most...