I agree with many of the other posters. It's a lot more fun watching a whole bunch of kids run around than just the one. In addition, having a number of kids extends the period when there are kids there. Eventually they become teens and start doing boring things like homework and chatting online instead of digging a hole to China. Then, of course, they leave home around 18 until their parents have died.

In addition, it seems a waste of five beds to have only one child.