I haven't lived in Mt Isa, but my dh and his entire family and 90% of his friends grew up there. Most still live there. They are all bringing their children up and don't have any concerns with regards to the lead. To be honest, when I mentioned the part where you said 'Mount Isa has the HIGHEST rate of childhood cancer IN THE WORLD', they really didn't believe that. Could be true, but he, myself and a lot of people living in Mount Isa have never heard of it. Do you know of anyone that lives there? Perhaps you could talk to them directly about what it's like living in Mount Isa, and your concerns. Council, schools etc.
For me personally, Mount Isa wouldn't be a town I would move to without doing a lot of research about the place so you know exactly where you're moving to. I've been there to visit, and don't like it.