In sims 2 (and I assume in sims 1) you could play different families within the one neighbourhood. Sim 3 has made this harder to do because of the introduction of story progression - which means that while you play one family, all the other families progress in their own lives. So technically, if you wanted to play in the same neighbourhood as your son, you could, by going into the game and switching households at edit town, but unless you turn story progression and aging off, the other family will be different when you switch back again. It is possible to play with story progression and aging off, so that all the families stay the same, but that comes with some challenges of its own - I play this way, and if you're interested, let me know and I can tell you more about it. But even with story progression and aging off, some little things will still change, I guess because sims 3 is really designed for story progression.
In sims 2 you could only play a neighbourhood (e.g. pleasantview) once (but you could switch families easily), while in sims 3 you can have several games in pleasantview, but each pleasantview will be different from each other because they're seperate games files. So if you do want to visit each other, you'll have to play on the same game file, as I described above.
does that make sense?