Ok, now that I got that off my chest, I will elaborate upon the differences between a kit lens and a 1.8 prime. There obviously seems to be some misunderstanding.
Let's start with the basics. When you look through the view finder, the lens is wide open. That means, with a 1.8 prime, the aperture opens wider, so the view finder will be much brighter than with a kit lens. Now, the kicker is, the focus module also uses the image that is projected to the view finder. So, the image is brighter, the focus module works better, more shots are in focus. Now, the second kicker, a D5000/5100 has a pentamirror view finder, which is already darker than the pentaprism view finder of the D90. The D5100 is a newer model and I will say that it has comparable high ISO performance as it's big brother, the 'obsolete' D90, which can be found very affordable used. Now, for the third kicker, the D90 can utilize that $100 50mm 1.8 fully while with the D5000/5100 it is manual focus only. For the fourth kicker, manual focus absolutely sucks with actions sports. For the fifth kicker, a kit lens has a minimum aperture of around 3.5 to 5.6 depending on how far you are zoomed in. Let's assume you get the 18-55 kit lens. That means around 50mm, the kit lens will be at aperture 5.6 while the prime would still be at 1.8. Anybody want to guess how much of a difference that makes?
Schools out. To the OP, do whatever you want, but in the conditions you are going to be shooting in, while it may look bright, those conditions tax some of the best systems money can buy. You need every edge you can get, and that means you need a prime lens that has a max aperture of 1.8. You have two choices that won't blow your budget out of the water...a 35mm 1.8($220) which will autofocus on any nikon camera including the d5000/5100 or the 50mm 1.8($100) which will only focus on a camera that has a focus motor. In 35mm effective focal lengths, that gives you a choice between a 75mm 1.8 prime and a 52mm 1.8 prime. Because you are getting a crop body sensor, you gain a 1.5x reach. IMO, the 75mm efl is going to be a bit too short, but you can probably crop and get an image you can proudly display...the 52mm efl is just going to be too short.
Now for the sixth kicker, the D90 offers the ability to control remote flashes without any special gear...with the D5000/5100 you have to buy flash triggers. There are so many compromises with the d5000/5100 series and it costs so much money to overcome them, I honestly don't understand why anybody who is thinking they may want to grow as a photographer would even consider it.