Getting married at a young age will not make you poor, but having a baby when you are young will make you poor, poorer society, because the cost of raising a child until he grows is really a big money.
I think if a young couple is planning to raise a baby straight after their marriage, they should work even harder than other couples as the cost of sending a child to the university when he grows up would surely be much more expensive in the future, and I guess that is one of the reason why some young couples are not planning to have any kids until their careers is stable.