Install roller shutters. No one can break into the window then. If you are so concerned then put them on all the windows.

My eldest is 12 and had a similar window with access from the front. She’s still in there after 10 years. Older windows than yours. It depends on your neighbourhood. We don’t always lock the doors but if you live somewhere different a roller shutter is a good idea. Although you can “pop” a lot of them off at the sides with a jimmy bar but it is a good deterrent and breaking in would be noisy. It’s pretty natural to be worried about “silly” stuff when you’ve just had a baby.

I can’t see from the photo but if you don’t have a gate across the side access I would add that in. Besides a shutter other ideas would be a sensor light or alarm- being able to sleep peacefully and not worry about your little one is priceless.

If you are worried change the window for something a bit more secure that you can lock open. Your high fence will be a deterrent, Have a chat with your local police community liaison officer about the risk in your area

Good suggestions above. If your neighbours drive is exposed to their home, why would a bad person jump your fence to your home. Baby’s bring concerns that probably have never entered your mind before, but if you have a safe neighbourhood, then hopefully It will continue to be that. I remember the first time I drove with my first baby in the car. That was so weird.