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.
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.