I have set up a spotted black background (soft velours sheet from cheap clothing brand). As the darker portions of their clothes get less light, they tend to go black and 'merge' into the background. This is called (lack of) definition. To solve that, you can place a flash so that it's light brushes the subjects and creates an outline on the side you placed the flash. This outline defines the contour of your subject and that little outline also makes sure you can tell between the background and the subject. You can see clearly in the examples on the right:
Alright my dear wife, you were completely right (but just this once..). As a portrait photographer, I have spent way to little time photographing my own kids in a studio setting. I have always found that being able to capture the loved ones around you is the no. 1 value of photography for me. There's nothing like looking back at a photo (which is more or less eternal) and being able to say that I'm the one who shot it.
And if you would like to learn how I typically start lighting these kinds of shots, please read on.
I first start generally setting up my flashes to have a working setup: attach triggers, put in batteries, connect to a lightstand and place them in the right spot. As I'm in a small room with a huge portion of light coming through multiple windows from 1 side of the room, I have my key light (also called 'primary light' or 'main light') already there. So in cloudy conditions this means I've got soft light coming in directionally (soft and directional are both properties light can have) from this big window. Also, on the other side of the room there's a white wall where the sunlight bounces back from, so this could function as the 'fill light' to fill in shadows which would be too dark. Now, by placing the subjects (in this examples: my own children) closer or further away from window or wall, I can determine how much light falls on either side of their faces. Place them more to the window: the key light will get brighter and the shadow side of their faces will become darker. And vice versa.
Now this part's a little tricky: Light has a certain direction it travels in. The sun emits light in every direction, 360degrees. But most of this light doesn't travel through our window and into our room; only that small portion of sunrays which happens to have the direction of our window. All other light is filtered by the walls for instance. The advantage of directional light is that it allows you to model the light to your liking because it's only there where you want it to be. With non-directional light coming in from all angles, it's hard to create shadow fall-off, or create shadows at all.
For more info on this subject: Check out the book 'Direction & Quality of Light' by Neil van Niekerk.
If you place your flash for this effect, it's called a 'rimlight'. Check out the shot on the left here: It could have used a rim light on the left side, don't you agree?
So now you've learned about key light, fill light, and rim light! Great stuff. Thanks for reading and have a great day.