Some notes on meter
Most children's verse creates its major sound effects out of a pattern of syllabic accents, sometimes in conjunction with the total number of syllables in a line (in accentual-syllabic verse); sometimes not (in accentual verse). Accent, or stress, is not difficult to determine: it usually follows the "natural" stress of the words. Most English words have one strong stress; multisyllabic words may also have secondary and tertiary stresses. You can discover them by looking in a dictionary and seeing how they're marked, or simply by saying the word out loud. Once you've determined where the word stresses fall, read the line out loud. You'll find your voice naturally accentuates certain syllables--for example, we tend to elide prepositions and stress nouns. (Sentences like: "I told you to put the book on the chair, not under it," are an obvious exception.) You can mark stresses like this: /--/- marks the stress pattern for "multisyllabic." (/ marks a stress; - marks a weak or unstressed syllable).
Once you've determined where the stresses fall, you may also find that there's a pattern of stressed and unstressed syllables. The most common metrical forms in English combine the number of syllables with the number of stresses in a regular pattern.
Iamb: - / Anapest: - - / Trochee: / - Dactyl: / - - Spondee: / / Pyrrhic: - -
Note that the boundaries between the feet (one iamb, or one trochee, is known as a "foot") are arbitrary--they have nothing to do with the syntax or the word boundaries in the line. Rather, they describe (somewhat abstractly) a rhythmic sequence, or pattern, of relatively strong and relatively weak stresses. The number of feet in a line will determine the name of the verse form: iambic pentameter, for example, has five feet organized in iambic rhythm. Tetrameter has four feet per line; trimeter three feet; and so on.
Much children's verse does not adhere strictly to these Greek-named accentual-syllabic verse forms, relying rather on patterns of stresses unrelated to line length. Thus you may find tetrameter or trimeter, simply by counting stresses, but will not be able to determine the patterning described above. Accentual verse, which relies on a regular number of stresses per line, is an older verse form in English than the accentual-syllabic verse described above, and is often associated with oral or folk verse forms. Ballads and other narrative poems often rely on this older style of verse.
You may find the following children's poem helpful in remembering the various metrical feet discussed above:
Trochee trips from long to short,
From long to long in solemn sort
Slow spondee stalks; strong foot, yet ill able
Ever to come up with dactyl trisyllable,
Iambics march from short to long;
With a leap and a bound the swift anapests throng.
(Samuel Taylor Coleridge)
To scan the following verse, you would first mark the stressed syllables as follows:
/ - - / - - /
Hickory, dickory, dock,
- / - / - /
The mice ran up the clock.
- / - /
The clock struck one,
- / - /
The mice ran down.
/ - - / - - /
Hickory, dickory , dock.
As these markings will tell you, the verse alternates trimeter lines with dimeter: 2 trimeter, 2 dimeter, then one trimeter again. You might also note that the middle three lines are quite strictly iambic, while the first and last are strongly anapestic, but drop the unstressed syllables in the last foot.
Rhyme is also an important element of scansion, and of poetry in general. To determine a rhyme scheme, mark the last stressed syllable in each line (and the unstressed syllables that follow it, if any). Conventionally, the first sound is marked as "A," the second as "B," and so on. Often poems rely on partial or half rhymes, as in "one" and "down" above: the final consonants are the same, and the vowel sounds are closely related, so they can be considered a rhyme (technically, a "slant rhyme" or "off rhyme"). The pattern, then, for the verse above, would be: AABBA. Note that the rhyme pattern follows the metrical pattern: the trimeter lines rhyme on the A word; the dimeter lines on the B word.
Generally speaking in adult poetry we look for places where meter breaks down, where an expectation is subverted. In nursery rhymes and nonsense verse often the pleasure derives precisely from the predictability of the verse: without even knowing the meaning of the words, we can often predict what sound will come next. Metrical predictability aids in memorization, a key element of much children's poetry and older folk verse as well. Breaks in metrical pattern are sometimes used to comic effect in children's poetry; when a rhythm is established, breaking it--especially in order to insert a humorous word or concept--is often funny. Form and content, then, need to be considered together in order to determine the effect of meter and rhyme: meter by itself means nothing.