Higglety Pigglety Pop

This rhyme is often associated with the American writer Samuel Griswold Goodrich (who wrote under the name Peter Parley) from the mid-19th century. His version typically involves a dog getting into some medicine, sometimes described as pills or a julep. The rhyme is a wonderful example of playing with rhythm and sound, often written in a specific poetic metre called dactylic dimeter. Dactylic dimeter is a poetic meter where each line contains two dactyls ((a stressed syllable followed by two unstressed syllables). This results in lines with six syllables, and the rhythmic pattern creates a "falling" or "plodding" sound.

There isn't a deep moral message embedded here, it's more about the fun of the sounds and the amusing scenario.

There is also a well-known, but quite different, modern children's book and poem called Higglety Pigglety Pop! or There Must Be More to Life by Maurice Sendak, about his dog Jennie. However, the nursery rhyme featuring the dog and the medicine is much older.