A little girl lies awake at night, unable to fall asleep because her thoughts have grown too big and too deep for bedtime. The poem is short and simple, but it captures something many people know: that moment when the world goes quiet and the mind refuses to follow.
The final four lines carry the main image. Her mind doesn't just wander, it "had gone out for a stroll," as if it were a separate thing with a mind of its own, taking a casual walk before tumbling into a rabbit hole. The phrase likely nods to Alice's fall into Wonderland, which suggests a world of strange, endless questions. The speaker seems to watch the girl with gentle, amused affection rather than worry.
The mood is playful and light, helped by the quick rhythm and the tidy rhymes (sleep/deep, stroll/hole). Yet there's a quiet note of restlessness underneath: once you start thinking, it can be hard to climb back out.