Yukoncher - the Guardian is appointed by the court to represent the child. The Guardian almost always has a lawyer too (but I have never seen the need for this as most Guardians are very experienced and know the law inside out!).
The Guardian's job is to inform the court about what she or he thinks is in the child's best interests. The Guardian should be visiting the child and parents fairly regularly thoughout proceedings.
If the child is old enough, a very important part of the Guardian's role is to speak directly with the child and report back to the court. If the child and the Guardian disagree, the child can instruct his own solicitors but the Guardian will remain involved.
The Guardian writes interim reports and a Final Analysis for the final hearing - a very important document. Generally the court will take what the Guardian says very seriously and will have to give reasons if the court goes against the Guardian's recommendations.
I have met Guardians of variable quality but only a few I thought were really bad - one hadn't seen my client for 8 months!! before the final hearing and got all sneery when I cross examined him, saying it wasn't his 'job' to visit parents. I said it was his job to at least assess for himself what the mother was up to and how she was coping. I thought he was a prick, but he was the worst so far. The best ones are brilliant and are more than happy to stand up to LAs when they disagree with them.