What camera lense do I need?

I currently have an 18mm to 55mm lense. I want to find a good lense that would get good crisp photo's of my 2 year old son. I currently use a nikon d3000 and it does me fine. If someone could recommend a lense that would suit this purpose?

Your lens isn't terrible, but a nice lens for portraits on your camera is the 50mm f/1.8.It's under $200, too. (100 pounds) The 50mm f/1.4 is ultra nice, but twice the cost.

To be completely honest, I feel like that should be adequate.

I have to wonder if there's lack of sharpness because:

-The shutter speed is too slow and handshake is causing slight blurring
-Your son is moving and the shutter speed is not fast enough to freeze motion
-The auto focus point was not placed in the right location so the plane of critical focus is in the wrong place
-You are using the lens at its maximum aperture ( the kit lens is more sharp at smaller apertures / zoomed in)
-You are not sharpening your images

It would really help to see a photograph which you consider lacking in sharpness and knowing why you feel it is lacking in sharpness.

Without diagnosing the exact reason for the lack of sharpness I would hesitate to recommend purchasing a new lens only for you to discover the same problem still occurs. In many cases new equipment is not the answer.

I'm not sure what your knowledge or experience level is though, so you may already know the lens is the problem.