We've lived in Colorado for 7 years now, and aldo do not mess with the screens. Last year we lived in a 100 year old house without central heating, and the thought didn't even occur to me then, either. But this year, we bought a new house in an area with insane wind. Like seriously 80 mph + winds, and we've considered removing the screens in the winter time, but only to protect them and keep them from blowing away. But still, I don't know a single person who removes screens and puts on different windows in the winter. About a kid removing a screen: When my now 13 year old was 3, he did something (don't remember what) and I sent him to his room as punishment. He opened the window, pushed the screen out, and went into the backyard to play with the dogs. I remember being in the kitchen, looking outside, and being shocked he was out there. (And grateful his window was within the fenced area.). So IMO, it's totally plausible a 6 year old could climb out if my feisty 3 year old could.