My sister has just bought the Sony DSC-HX200V camera. She mainly uses the camera to take photos of views and portraits of children (for university work). Are there any lenses available to buy for this to make better quality photos? If so what?
That camera has a fixed 30x optical zoom lens, so there are no alternative lenses to buy for it.
There are third party wide-angle and close-up adaptors available that screw on the front, but that will likely decrease image quality by introducing additional elements in the optical path. I would not recommend buying one of these until you find you really need it.
The built in lens provides a 25mm equivalent field of view at the wide end so that should be sufficient for landscapes.