People have children, because people around them have children. This means that a blip will extend into a boom, as people suddenly are surrounded by happy couples with cute toddlers running around.
For example, my wives circle of friends didn't want to have children. Then we got our two girls, both of which were very well-behaved and cute. Two years later all of her friends had a child, and one of her friends even confessed that she had hated children before she saw how absolutely adorable our kids were.