Months, Metre and Rhyme

Two nights ago, my lovely wife was lamenting about the awkwardness of the standard poem used to teach kids (and many adults) how many days are in each month.
You know -

Thirty days hath September,
April, June, and November.
All the rest have Thirty-one,
Except for February.


I mean talk about elegance and brilliance.
So me, taking a (graduate level) class on poetics and poetry, and being the aspiring literary artist that I am, endeavored to make the poem better. (You can tell we have pretty hoppin' social lives around here).
This is what I came up with -

Thirty days are in September,
June, and April, and November.
Twenty-Eight in February,
But be careful, it can vary.
All the rest have thirty-one.
Who knew that months could be so fun?

This is not what I originally came up with.
At first I left the first two lines (or couplet) alone. It was the same as the original.
I also, had "But beware" instead of "but be careful."
In both instances I made changes in order to create a regular rhythm and metre.
I wouldn't have had words for it before this class, but you can feel it when you read it, especially out loud.
Just now, I tried to make the second-to-last (or penultimate) line eight syllables like the rest, but it just didn't work.
I think because almost all of the lines start out with a first stressed syllable, and the line wanted to start unstressed which didn't want to flow from the unstressed syllable ending the line right before it.

Well, I think I've bored you all enough with all of the deconstruction, and it's past my bed time.
Good night!