For instance, I have one son who could sleep 14 hours a night and the other one, who is almost one year old, likes to sleep only about 7 hours a night.
Children learn to sit, crawl and walk at different ages and in different ways, too.
These children developed speech sounds differently. We also know that frequently these children had no direct need for speech therapy too. With these questions aside, it has been shown that children do have similar patterns of development, generally speaking, as far as speech sound aquisition goes. Children learn to do eassier tasks before more difficult ones. The same holds true for speech sound development.