Islam gives human life the highest degree of importance and considers it is sacred. That is why we find many Quranic verses and Hadeeths encouraging marriage and having children.
The term of " overpopulation" is not accepted by us at all. Who has the right to put limits to population then to claim that it is over?
If sources are utilized properly, there will be no question of overpopulation. Islam encourage utilizing the sources in better ways which will improve he quality of billions of human beings.
Islam emphasize on the quality of life which is possible through fair distribution of the sources among people and filling the gap between poor and rich through Justice.
Those who claim overpopulation in the western media don't act against wasting millions of tons of food committed by big western companies and governments just to gain more profits ignoring he need f millions of poor human beings.
If the sources are maintained and distributed in a just and fair way, no human being will remain in need, as Imam Ali (AS) said: No poor person starves but because of the selfishness of a rich.
Islam not only encourages Muslims to have more children, but asks them to look after their children in a proper way and bring them up in the best environments and treatment as much as possible.