Actually, children with older siblings, who also have limited contact with their age mates (ie: daycare) tend to lag in speech, which has been observed scientifically, but I can provide anecdotal evidence, as well. My friend's youngest brother didn't speak till he was about 3. The doctor was quick to identify the problem, which was that his older siblings were quick to respond to him when he pointed at things that he wanted/needed. He never had to verbalize his his wants or needs. Once they stopped he started speaking very rapidly, in full sentences. The same thing happened with my little sister, although my mom didn't consult a doctor, and now you can't get her to shut up. ;-) Finally, I work with children and have observed this phenomenon from an adult perspective, as well. Don't always be so quick to attribute problems to the wonderful and NORMAL range of behaviors in child development.