Actually, most parents do invest their money instead of save it in banks.

But, they choose the safe investment that the gain can't hedge against school and medical inflation, usually a country has 4% inflation rate, but the school and medical inflation rate are around 10%-15%.

These parents choose to invest their money in time deposit (5% APY), ETFs (7% APY), gold (8%) or stock (depend on the stock). The thing is, most stock didn't bring a good amount return for long term, moreover these parents mostly choose investment that can't hedge against inflation, that's why the poor stay poor.