I do believe there are (or will be) serious problems if the one-child policy continues as it traditionally has been. One of the most pressing would be a point where you would have a high number of old people and relatively few young workers. This is what plagues many western countries, but alas they are a bit better equipped to handle the problem. China still has so many other pressing issues to allocate resources into, if not also having to handle this ageing crisis.
Still, I have complete confidence in that the Chinese government is well aware of these problems, and as soon as the rationale for the one-child policy is seen as less of a problem than ageing population, unfavourable sex ratios etc. the one-child policy will drastically change or disappear.
Already I read that the policy will be slackened substantially in Shanghai. Also, certain measures have been taken on the countryside to alleviate some of the most serious problems (families allowed two children if the first is a girl). And as always, the minorities are allowed to stay outside the policy. It will sort itself out, gentlemen. Have faith. The Chinese authorities aren't ideological idiots.