If something nefarious had happened and you were responsible, I think you’d tell a story much more favorable to yourself than “we were asleep and maybe not properly supervising.” That being said, when my kids were little, they got up before me and entertained themselves. One time my son made himself cereal…in the colander.

But generally it was just fine. My bedroom was 10 feet away from them.
One thing I wonder…why did they put on their boots? Was it muddy? Were they expecting their feet to get wet? Are those the only shoes they could easily locate? I feel like they impulsively went outside because they saw someone or something that was interesting. (The backpack thing is unimportant. Lots of little girls do that. Of course, it’s also possible that she thought she was going to school.)