2.A very very simple bur powerful portrait.....it does not make any difference that u photograph more of children or adults....They should represent the variety of light and shade, which will make a portrait different from one another----changing and handling the lights carefully, giving emphasis on every part of the face subdueing or enhancing the features.
3.....THERE ARE WAYS U get the light artificially or from nature.....In case of above, it is simple light from window at left, which provides less contrasty and soft light.
4....U can move ur subject all sides where the light suits according to ur requirement, sitting him/her on a stool. Since there is low light in homes, a sturdy support to avoid camera shake is necessary.....U can use tripod or improvise from some goods/hard/stiff material/beanbag to support the camera steadily.
5. Background is as important as the subject which I did here in photoshop to liftup the face and I feel I was successful in that. There are very important whites behind the guy which help lifting up of the face surrounding with dark areas of the frame......Do it urself and let me know.