Some children, more often boys, develop speech more slowly. I wouldn't worry about it. I have a friend who worried about her first son's delayed speech and had him tested. There was absolutely nothing wrong with him. His younger brothers (and my middle boy) were the same way. When they started 3yr. old pre-school, they spoke very little (her one boy had a vocabulary of 3-6 words). Half way through the school year, all these boys were talking up storms. I have 3 children. My oldest is a girl who spoke clearly and plentifully early. My second is a boy who was slow in speech development and was not as articulate (had the very normal difficulty pronouncing certain sounds-a speech therapist at your local elementary school can tell you developmentally appropriate difficulties). He had someone to talk to, but just wasn't ready (or didn't want to). My third child is a boy, and he developed more moderately (in between my other 2). People will try to say it depends on whether they have siblings, but I don't believe any of it. Kids develop at their own rates. Please don't worry about your son. It is not uncommon for him to not be speaking a lot right now. He obviously understands your words, so it sounds less a problem of having an au pair that speaks little English, and more a case (which is common and normal) that he's going to be one of those children who, when they start speaking,will speak in multi-word phrases or even possibly sentences. If you still don't have peace of mind, or have a gut feeling that's something more is wrong, you can most likely talk to the local school system about having him tested. Our school system (MD, AA county) has what is called Child Find. I will warn you, though, that a friend of mine who used this service got pushed into other services she felt (strongly) that her child did not need. Now her son has a record going into kindergarten, which could possibly bias some teachers.