If a five-inch ball can fit through any window opening, then the window guard has not been put in right. If you have a different kind of window , special window guards and stops approved by the Health Department must be used. If your window guards aren't installed yet, keep your bottom windows closed. Open only your top windows for fresh air. Furniture that children can climb on should not be near windows.
Some babies can climb up on furniture and crawl through open windows even before they can walk.
Your child could be hurt or killed falling out a window, even from the ground floor. If you own your house, you can have window guard installed or do it yourself. If you rent, you can ask the owner or landlord to put in window guards. You can offer to pay for the window guards. And you can ask the landlord to let you have them installed or to let you do it yourself.