Best setting for portraits with natural lighting?

Just wondering what you believe is the best setting to take portraits in natural lighting.
I have a nikon D40 with a AF-S NIKKOR 50mm 1.8G

photographing young infants with natural lighting mainly inside.

"best setting"? Are you actually expecting us to provide you with the correct aperture, shutter speed, white balance, focus, etc?

Perhaps you have never ever used your camera before, but it doesn't work that way. It changes all the time, depending on the light, the background, the subject etc.
That is what learning about photography is all about.

THERE's NO MAGIC SETTING.

The settings change with the amount of light you have (the Ambient light).

The easiest way is to use Aperture Priority (A on your mode dial), set the aperture with depth of field in mind, set ISO with noise in mind, the lower the better, half press the shutter and the camera will tell you what the shutter speed will have to be to get a good exposure.

Indoors it will probably be slower than you need, expect anything from 1/30th of a second to half a second or so depending on the light level.

You have choices, you can open the Aperture to let more light into the camera, but the depth of field will be narrow and focus has to be more accurate, you can up the ISO, which makes your camera more sensitive to light, but at the expense of more noise in your image, or, best of all, you can increase the amount of light.

A Pro will always choose the latter, as then they are in control of light, it's direction, it's intensity you can create any lighting you want. A large soft-box will mimic and look exactly like the light you get from a large North facing window an I can control it's angle, shutter time is effectively the duration of the flash (less than 1/1000th of a second), I can use any aperture I want, and noise will be non existent.

Best setting is YOU LEARNING ABOUT HOW LIGHT WORKS and the basics of photography…

you can spend a fortune on the camera and lens, but if you don't know what you are doing, you'll still take bad photos…

If I asked this question: "I live in Indiana so what's the best way to get to the next state?" you'd probably tell me you needed to know where in Indiana and what state I want to go to. Illinois? Michigan? Ohio? Kentucky?

There are no "best settings" for natural light portraits because there's no way for anyone except you to know the lighting conditions you're working with. That's why your D40 has a built-in light meter - so you can meter your subject and set aperture and shutter speed yourself based on the ISO you're using - in Manual Mode.

It might be a good idea to once again READ & STUDY the Owner's Manual for your camera and see what it suggests for indoor portraiture using available light.

I can, however, tell you this with no reservation - trying to use the 18-55mm f3.5-5.6 zoom lens indoors with available light is going to prove frustrating and will require a high ISO setting which will result in pictures with a lot of digital noise.

Digital cameras are not magical. They are bound by the same Exposure Triangle interaction as the old time film cameras were. The only advantage a digital camera has is the ability to change the ISO any time you want or need to.