retro stops to upvc windows

[str]

we have upvc sash and case windows and the wife would like stops to the windows so that she can leave the windows open without the fear of the kids opening the windows further and jumping out!

anyone any ideas where i can source something like this?

I guess it would need to fix to the upper casement so that it prevents the lower sash from rising too much?

 

[The Bullet]

After supplying a job that we had to go out to and retro fit sunk in restrictors to when our customer decided they did in fact want travel restrictors (nightmare to fit after the steel is in the sashes.), we now fit them as standard. They are very unobtrusive and easy to use. You could try and get a company to fit them for you - they are known as shark fin restrictors. Any other restrictor is probably going to ruin the look of the window, but i'm sure you can get some face mounted ones that will do the job.