After being asked this question by worried parents for years, I stumbled across this article on the Vancouver Sun.  I hope this gives some parents some ideas on what to do if they are worried their child might fall through the screen.

Tips to protect young children from the B.C. Ambulance Service and BC Children’s Hospital:

• Move household furniture — especially cribs and beds — away from windows to discourage children from climbing to peer out.
• Install window guards on windows higher than ground level. You should not be able to open upper level windows more than 10 centimetres (four inches). Children can fit through spaces as small as 12 centimetres (five inches) wide. Ensure there is a safe-release option in case of a house fire.
• Don’t underestimate a child’s mobility; children begin climbing before they can walk. If you have children in the home, make sure to install window guards as early as possible.
• Don’t leave children unattended on balconies or decks. Move furniture or planters away from the edges as kids can climb up and over them.
• Talk to your children — in an age appropriate manner — about the dangers of opening and playing near windows, particularly on upper floors of the home.
• Remember, nothing is better than ongoing supervision. Don’t leave a young child unattended or rely on a safety item to keep them safe.

Read more: http://www.vancouversun.com/life/Tips+parents+prevent+falls+from+windows/7108602/story.html#ixzz23uwa2mlO