Repeat a rhyme and loop on the vowels
Retina, 45 bytes

~(K`A\EI\OU
L$`\\?(.)
./$1/i&amp;$*\T`Vv`5*$&amp;$L$&amp;


Try it online! Does not count y as a vowel. Explanation:

K`A\EI\OU


Replaces the text with the literal string A\EI\OU.

L$`\\?(.)


Matches each letter optionally preceded by a backslash.

./$1/i&amp;$*\T`Vv`5*$&amp;$L$&amp;


Outputs a line of Retina code for each letter.

~(


Evaluates the generated code (shown below) using the original input. The . causes the code not to output the (final) buffer. The /&lt;vowel&gt;/i&amp; causes the rest of the line to run only if the input contains the given vowel (case-insensitively). The * causes the result of the line to be ignored, so that the next vowel can be tested. The \ causes the result to be printed on its own line before it is ignored. The T`Vv`AAAAAa transliterates uppercase Vowels to AAAAAs and all lowercase vowels to a. \A is an escape that refers to ASCII 07 (BEL), but E, O and o are built-in character classes that needs to be escaped to give their literal values (e is not a character class, but fortunately it is also not an escape.)

./A/i&amp;*\T`Vv`AAAAAa
./E/i&amp;*\T`Vv`\E\E\E\E\E\e
./I/i&amp;*\T`Vv`IIIIIi
./O/i&amp;*\T`Vv`\O\O\O\O\O\o
./U/i&amp;*\T`Vv`UUUUUu