Remember the specific needs of the original poster. He is seeking images of his kids for his wife's scrap-booking. I assume those images will be 3.5 x 5 inches or 5 x 7. I doubt she will use 8 x 10 photos. So the issue is how to get those size images using a D7000 and an 18-105 lens.
First, set your lens to 105.
Second, crank up the ISO as much as you can stand. 1600 should work fine, 3200 may work and some people may even find 6400 acceptable.
Third, shoot in S mode with the shutter speed set at 1/250th, 1/320th, 1/400th, 1/500th of a second and see how low you can go and still stop the movement to an acceptable level.
Now you have some parameters to work with. Set the camera to the highest ISO you can use, set the shutter to the lowest speed you can use and take some photos at those settings. These will be the best images your current equipment can produce for you as an original photo. But your camera has one more option: the super number of pixels in that D7000 sensor will allow for a great deal of cropping as long as your final image will only be printed to 5 x 7. What is the cheapest way to crop? Using something you already have: Windows Photo Gallery. How much can you crop? If you crop to half the image you have the same size kid as a 210 mm lens would produce. If you crop to one third the image you have the same size kid as a 300 mm lens would produce. I think the D7000 will allow you to crop to one half or one third the original image and still have enough image quality for a 5 x 7 print for a scrapbook and I provided some examples. So try some cropping. Print the results see if this technique will allow you to produce the scrap book image you need with your current equipment. Maybe or maybe not. You can only tell if you try it.
Because we love equipment and lust after the latest and best, almost everyone here quickly leaps to the conclusion that the original poster "needs" to spend $500 to $2500 to get adequately close-up images of his kids playing sports for 4 x 6 prints for his wife to use in a scrapbook. I am challenging that assumption. I am suggesting he may be able to get what he wants without spending one penny.
There is nothing "wrong" with spending $500 to $2,500 on a new telephoto lens. But the impression created from many of the responses posted is that it is "needed" to get what this guy wants to get for his wife. I challenge that. He may be able to produce what she needs without spending a penny. That is my point and no one else explained that to him. Someone should.
As for whether or not all the money I spent on equipment was a waste of money the answer is "probably." If I had more talent I could produce great photos with a point and shoot camera. Equipment doesn't substitute for talent. Sure the equipment lets me do things I could not do without it, but being able to shoot in lower light or at a wider angle or with a greater telephoto doesn't itself produce a better image.
Look what this guy does with an old outdated point and shoot.
I can spend thousands of dollars on Nikon equipment and $700 on Photoshop but doing so won't automatically get me better images than this guy produced with a point and shoot. I love my equipment and want one of the next generation Nikon bodies which will be out next year but I have to admit the limiting factor is my skill, not my current equipment.