I remember learning this as an adult - having gone to French school, I was taught the knuckle method (start at the first finger knuckle, count knuckle (jan) - in between knuckles (feb) - next knuckle (mar) - in between (apr) and so on; when you get to the end of your hand (July) start over (August). The "knuckle" months have 31 days, the "between" months have fewer, and all you have to remember is that Feb has 28 or 29. NO rhyme but lots of reason!