Double glazed uPVC windows are resistant to impact and it would take a real effort to break them.  The glass is treated and toughened so that it is extra resistant, additionally, with double glazing there are two panes of glass to break through.

A variety of different glazing finishes are available from your installer and can be specified at the time of specifying your new window installation.  Different types of glass are available for many purposes, from purely aesthetic styles with bevelled edges and stained-glass areas through to more reflective and self-cleaning finishes. 

While the nature of the windows and frames does mean that they are less prone to breaking than traditional windows, they can still break under extreme circumstances.  If you specifically require a shatterproof finish, you can speak to your installer, and they will be able to advise you about the different glass types available to ensure that you can find a set of windows that meet your needs.