Speaking as a Clarinetist/Saxophonist (please don't tell anyone!) I don't think you can go wrong with either a Yamaha (my preference), B&H or Buffet to start with. In fact, Yamahas are used by some of the very best pro players out there.
Kids can be funny about secondhand instruments, but if you can I'd try to get a wooden Clarinet. The sound is a lot warmer and fuller and it would be an instrument that you can grow with.
Beginner instruments are exactly that; beginner instruments. When you develop your embrochure and own sound, you really need to move to a better quality instrument. That said, the Yammy's are very good quality.
As mentioned above, it's important to get the right mouthpiece too as it will make a world of difference. Beginners mouthpieces have a large bore which is easier to blow and play louder, but they do sound very honky after a while!
If I can help any more, please don't hesitate to ask.