Matty I applaud you for this Question

it is one of the best I have read here well done

There are many kids that fall out of windows in China and all over the world and it is a tragedy that could so easily be avoided.

you could get a window grill made at one of the many street metal working shops

and get it painted.

then just push into the window frame and wedge it in place.

I have been to friends places like you described and worry about it as well 

China is not known for it's health and safety

Mine doesn't have any windows. When I ask at my School about it, they told me there is a 'Western' safety issue.

Chinese learn fast, I would say.

I own an apartment on the 20th floor, all our windows are about 90cms x 30cms and open past 90 degrees, i.e. as wide as possible. Falling out would be VERY easy, the only 'safety' is a 100cm wide ledge about 30cm high, (so easy to sit on climb on, play on) in front of the window.

 Dangerous? Not in and of itself but the potential is huge.

However, I don't like the Nanny state, life is dangerous and the best way of overcoming danger is to educate so it is my responsibility to make sure my daughter doesn't go near the windows and knows why, (she's 2 and has learned that lesson already). I wasn't happy in the UK with the overbearing "that could harm a child, ban it" attitude to so many things, (which, for harm to actually happen, would often require a process more complicated than nuclear fusion), yes China seems to have gone the exact opposite, but that's workable, it just means I know it is MY responsibility to ensure the safety of my family, not some remote impersonal Nanny state. What I do I ask / expect is that there are no hidden dangers that I cannot prevent (i.e. contaminated milk, incompetent teachers, lead based paint on toys, etc)