Meet the nappers
Si Esta takes the afternoon sleep entirely seriously, which is the whole joke and the whole method. The Cat Nap teaches the perfect nap curl — circle, curl, and be asleep before anyone notices — with her purr as the soundtrack and one bell tinkle as her eyes close. Little Kip never makes it past the second page, and Sloth to Sleep gets there slowly, which is also a way of getting there.
How nap time stories differ from bedtime ones
A nap is a shallower thing than a night, and it is trying to do less. At bedtime the job is to get all the way down and stay there until morning; in the afternoon the job is to get somewhere quiet for an hour and come back up cleanly, without the heavy, cross waking that a too-deep nap leaves behind. So nap time stories are built to stop short on purpose. They settle, they slow, and then they simply hold.
The second difference is the light. A night story descends into dark, and the sky in it comes down rung by rung; the daytime is still going on outside a curtain during a nap and pretending otherwise never works. Ours keep the daylight in the picture and do the work with pace instead — slower and slower, the same phrases returning, until the picture is barely moving at all. The third is what happens at the end: no goodnight roll-call, because nobody is being said goodnight to. It just goes quiet.
Shorter, lighter, and it stays light
Nap stories stay on the upper rungs of the Sleep Ladder — settling, a little sleepy — because an afternoon sleep is a shallower descent than a night one. The short pieces are made for exactly this: half a minute to a few minutes, and then quiet.