Do not have three kids if you can help it. There is no such beast as a five seated car despite what you may believe.
Oh come now, they're perfectly fine until you get around age 12 or so, and there's always the minivan option. Minivans are the best with three kids, because two have those nice single seaters to themselves, and the third has the entire back to lounge about in, and there's usually room to haul a friend around.
And as to the middle child being lonely, well, that might be true in my family (I'm the eldest of 3). I know that in any argument, our middle was usually out-voted (the eldest has to look out for the baby, after all). However, she's compensated (perhaps over-compensated) and grown up to be the most social out of any of us, so I think it could go either way.
As to whether or not I want to have kids, I definitely desire to have at least two kids and preferably more. I know people keep talking about overpopulation, but in most industrialized countries the population is stable or even decreasing. The reason the US still has its population growing is almost solely due to immigration. And it's not like we're at all short on food; modern occurrences of starvation are almost solely due to distribution, economic, and political problems. Energy is a different beast with real problems, but I'm getting off topic and rather rant-ish. One of the reasons that I really want kids that I don't think anyone mentioned thusfar is that I want my parents to be grandparents. Strange, I know. My parents aren't the type to say things like "When will you get around to making me grandkids," but at the same time, I feel like it's something that would really bring them joy in their twilight years. And, knowing how much effort they put into me, I feel like I should at least give them some security that their progeny will continue for another generation.
However, the question of whether or not I desire kids is completely different from the question of whether or not I want kids. I know almost exactly what you mean, Zangi. The idea of that much responsibility, quite frankly, terrifies me. Of course, this is balanced by the terror of dying cold and alone. I'm afraid I'll end up like my dad, who rarely ever socializes or even leaves the house; his family is his connection to the world, and basically what keeps him going from day to day. There's other things that tip the balance towards the "no child" side too, though I'd prefer not to mention them.
However, really, I try to not think too much on this. I'm going to be terrified no matter what I choose to do. And plus, there are more important things to do. First, a wife and a career with an annual salary. Then a house (not a big one, but a house). Only then should I start really worrying about kids. Of course, that thought doesn't stop me...