Would a 4-5 yr old read (or look at the pictures) of a picture book under the covers with a flashlight (in lieu of sleep)?

I know the idea of a kid with a flashlight under the covers is oft-used prototypical imagery (and that's OK with me) BUT at WHAT age do they do this? I know I did it but I feel like it wasn't until older... I don't know.
I do have to swap out the Mad magazine parody in favor of a picture book (4 yr olds wouldn't be reading mad--wouldn't get the joke)
I have to nail the age logistics.
HELP!