Nikkor 18-105 VR in dim light?

How good will a Nikkor 18-105 VR be on a D90 for

a) night/dim light photography
b) macro photography
c) kids photography

Have you checked the specs? The bottom f/stop is 3.5 - not very good for low light unless you're doing time exposure - then it would be fine.

This is not a macro lens so no. Macro photography requires a macro lens.

Kids photography? Fine if you have enough light - say out doors, a very well lit room, extra lighting in a room or flash.

It is clear the you have not taken the first steps to learn how to use your camera.

The first would be to sit down with your camera in one hand and the user manual in the other and learn how to use your camera. This can take a few months The other would to take a class in photography and learn how to use a fully adjustable camera. The second method will be quicker, lead to less frustration and prevent you from learning bad habits

That said, the 18-105 mm lens is a decent lens.

You can shoot your kids in daylight with no problems at all. YOU just have to learn how to use the camera and lens

You can shoot in low light, but you will have to increase the ISO in the camera to at least 3200

Macro photography will require you to buy a macro lens like the 60 mm f/2.8 or 105 f/2.8 macro lenses

You can buy special diopters (about $60 for a set of three) to allow you to focus closer to a subject, but they have issues with focus at the edges of your image or lens AF extension tubes (about $100)

It's a slow.normal lens. So nothing on your list will work well with it. It's a nice ~go hiking with friends and look introspective under a tree~ lens. But unless it's sunny and things are about 3ft away, that lens simply won't be good enough.

A- For long exposure it will be ok, for fast shutter speed, not good at all. You'll need a lens with a wide aperture such as the 35mm F1.8, 50mm F1.8

B- not good at all, you can't do macro since it is not a macro lens, you might be able to do some proxy though, but that's way far from the macro result. For macro you need macro lens with 1:1 ratio such as the 60mm F2.8 or Nikon 105mm F2.8vr.

C-Yes you can, but you won't be able to have beautiful blurry background like a lens with aperture such as F1.4, F1, 8, F2, F2.8.

While the others are correct, please note that it is not necessarily a bad lens, it is just typical of the kit lenses you get with many DSLRs. It is a consumer-grade all-around lens.

You can augment your low-light needs with a flash. Even if you bought a fast 50mm f/1.2, at some point in low light, you would still want a flash.

And I mean an external, more powerful flash such as a SB700. The on-camera flash is better than nothing, but it is not a high-performance flash (nor is it intended to be).

Macro is out. You can however get a nice set of extension tubes and then use the lens as a macro.

Any lens from about 50mm to 100mm is fine for photographing kids and people. You don't want to use the 18-35mm range of the lens for photographing people as the perspective distortion inherent in those focal lengths will make for unnatural photos.