She was 3. This was like nearly 15 years ago. It was "common knowledge" where I grew up that kids that age need a nap. Another interesting story involving her: she had two older sisters, and I would babysit them too sometimes although most of the time I just babysat her. One time when I was babysitting her and her siblings, her sister got violently ill really suddenly, she got a really high fever and started convulsing. I freaked out and tried to call her parents, but her mom was at a funeral and her dad was at work (he was an army doctor, but stationed locally) so neither of them answered. So I tried to bring down her fever, made her drink water, and generally panicked. None of the other parents of small kids in the neighborhood were home and calling an ambulance would mean leaving the other two kids unattended, so I didn't know what else to do. Anyway, then the littlest one came up to me and said "I'm going to play barbies while (sick kid) is shaking herself." Which brought a tiny bit of humor to the situation and then profound existential angst because she had no idea how good she had it, she had no idea what death was, and I was seriously freaked out about her sister's condition. The kid who was sick got better tho! So it all worked out fine in the end.
Those febrile seizures are terrifying, and it seems miraculous that usually there is no damage. Even knowing that does not make it any easier to watch.