Window locks for PVC window?

[Manfwood]

For the summer will need to buy some window locks as DS only has one large window in his room and i worry about him climbing on to the window sill and falling out - i've looked in M/care and John Lewis and only seem to have the sort that you have to screw in - i.e. for wooden window frames and didnt know about locks for PVC/replacement windows?

Any idea if they exist or what did you do if you had this type of windows?

Thanks a lot

We just kept the window locked.

In our old place though we looked into having windows fitted as we didn't have them and the company said they could fit limiters which allowed the window to only open to a certain width so it might be worth contacting a double glazing firm and asking if they can be fitted retrospectively.

Forgot to mention that i would not leave the window open when he was around but in the summer will need some ventilation!

Any more suggestions would be gratefully received. Will try Safety First website if can find!