RE: So when do they talk?
There are no language milestones before 18 months, and the "milestone" for 18 months is 10 spoken words or protowords. But it can be totally normal for them to have VERY limited expressive language until 2+. A far more important milestone is receptive language (what they understand). At 15 months, a child should understand a great deal of what is spoken to them. By 18 months, it should be a great deal more. By 2 years, they should understand most everyday conversation, even if their spoken language is very limited.
But there is such a huge range of normal. I know one kid who was talking in complete sentences at 13-14 months. My DD has expressive language delay, and has only recently starting talking in 3-4 word sentences (of limited intelligibility to those not "in the know" for her speech). But generally between 18 and 24 months, most kids go through a sudden language spurt where practically overnight start acqiring dozens of words a day. Its really miraculous to watch!
Beth, mom to older DD (8/01) and younger DD (10/06) and always missing Leah (4/22 - 5/1/05)