The main problem that a situation like this would cause to a country is that it would mean a small workforce. The workforce of a country is the population that produces goods and wealth. The economy relies on these people (working adults), and if this population reduces, the country ends up with a large dependent population and a small population to sustain the economy. This can lead to serious social and economic problems.
The independency ratio increases heavily . Or in other words it causes the work force to shrink which eventually leads on to inequalities, children labor increases and the age decreasing and retiring at later rates.