Unfortunately, in a world defined by generalities, we're going to have to boil down to a few hard details. But it will help settle some of the questions you have and really determine if you need more equipment or not.
One of the things that is most important to understand is the general limitations *around* your photography. First off; most concerts do not allow flash. This is is your first decision point.
If flash is allowed - great!
If flash is not allowed - okay - we know that's the first limitation.
The second decision point - exactly how close are you to the subject?
Five rows can vary depending on the venue, but let's assume a 7-10 foot dead space from the foot of the stage to Row 1. Every row is roughly 3 feet "deep" heading to the back of the venue. That's 15 feet + 10 feet = 25 feet. Assume another 5 feet minimum because the performers are *not* at the edge of the stage. That's now 30 feet roughly.
The third decision point - exactly how do you wish to "frame" the subject? This means how big do you want the subject to appear when you are looking through the viewfinder. This is not an exact ratio because the camera you have has enough resolution such that you can crop the photo afterwards using your editing software so that you can further isolate the subject. But this is a good starting point. You don't want to crop on the PC unless you have to. Everything that you can do in the field/on the camera is really the most optimal place to do it. For this we will need a bit of math but nothing fancy.
Let's assume the subject is a child about 3.5 feet in height - this would be typical for say a 6 year-old boy (very general statistics nobody quote me on it please - we're strictly operating rule of thumb here). In order for that child to appear to fill your viewfinder, meaning you are seeing their feet to their head or full-length as shutterbugs would say, you'd need a lens that can reach roughly 200mm if you're at 30 feet from where they are. Your current lens doesn't reach that far.
Now, I mentioned earlier, you can crop with that camera because it has enough resolution, such that you can "zoom" into the photo on the PC and it will still look fine on the screen and on prints (no pixellations or blockiness). But you need to understand that at that range in the fifth row, you're going to get group shots, not isolated subject shots. If that's what you're expecting, great. If not, we need to talk about some tactics or new equipment.
Obviously, the easiest way to solve the framing issue is to get much closer to the stage. Every row you get closer means you can isolate the subject a little more. Even at row 1, your lens is still not optimal for the task, but instead of a group shot, you're now likely to get the subject and maybe the people directly next to him/her, instead of six or eight people.
Best scenario requiring little to no additional expense - you are allowed flash and you get seated as close to the stage as possible.
Scenarios requiring some expense - you are allowed flash, but you want to get more subject isolation. You should consider buying a complementary lens to the 18-55. I would recommend the 55-200mm VR, which gives you that optimial framing that we calculated above. So even if you're seated in Row 5 or maybe a little further back, you can still isolate the subject using the long end of the 55-200.
Scenarios requiring larger expense - you are NOT allowed flash. Ugh. This means consideration of some the lenses DrBee recommended AND getting as close to the stage as possible because those lenses still are shorter than 200mm.
Scenarios requiring mucho expense - you are NOT allowed flash AND you wish to isolate the subject. I think you should consider very carefully before you go down this path. This reuqires purchases of specialized lenses that are not cheap by any means - minimum point of entry here is anywhere from USD900 to USD1700 depending on whether you go used or new and what features you might want.
If you can clarify the flash and seating scenarios, we can focus on what specific tactics and if any additional equipment is required.