You need lights. Lights are important. You can provide light any way you desire and can afford. That means thousands of dollars for a Profoto pack and heads, or $50 at the local Home Depot. Or many, many options in between.
Th most inexpensive lights are going to be drop lights, work lights, or trouble lights. Preferably the kind with the aluminum reflector, about 10-12" in diameter. For a small room, put large CFL (fluorescent) bulbs in them, as they won't generate any heat that way. At least 2, maybe 3 of these will be good to start with. The lamps have a spring clip on the back to hang them on whatever is handy, which also makes it easy to move them around as needed. Remember that you can bounce continuous lights too, they don't have to point right at the subject.
A stool or chair for posing. Maybe a table. Backgrounds are good, but not absolutely necessary. A tripod. A cable release for your camera, preferably long enough so that you aren't stuck behind the camera. This allows you to interact with the subjects, but still capture the expressions you are trying to get.
If you want your setup to *look* a little more "professional", you can get a hot light kit at B&H for $65 that include what is basically the work light mentioned above (with a handle and stand mount) a light stand, and umbrella. It comes with a 500 watt tungsten bulb, which will be very bright but will also put out a ton of heat. Replace that with a 35-43 watt fluorescent, and it will stay cool. Get a couple of these kits, and away you go. http://www.bhphotovideo.com/c/product/414532-REG/Impact_FL_500_KII_One_Light_Umbrella_Kit.html#features
There are also tons of them on ebay...