Here are the lyrics to a song I wrote for a Mother's Day program a few years ago. It's not great art, but it fits your category. (Each verse represents at least one person in my extended family.) If you would like the tune, let me know. (If not, I won't be offended.)

Here's To Mothers (They're All About Love)
Words and Music by Jeanene Pratt, © 1994; 1995

She may be little more than just a baby herself,
a teenage mom raising kids with little help,
but she won't love those babies any less for all of that;
She's a mother-- that's all there is to that!

Chorus: Mothers! There's just something about 'em.
Mothers! Where would we be without 'em?*
Mothers! The poets rightly tout 'em.
Here's to mothers--they're all about love!
Here's to mothers--they're all about love!

She may have raised five kids, a husband, and some dogs and cats;
Perhaps she's never "worked,"--I mean, of course, except for that!
Perhaps at times, she wonders what else she might have been,
But she's a mother, and she loves what that means. (Chorus)

She may have had her own career and raised her family too
And keeps her youthful spirit even now at eighty-two.
Her kids just throw their hands up, 'cause ma won't act her age!
This great-grandmother is still on center stage! (Chorus)

Perhaps she never bore any children of her own;
She just takes in strays and tends to those who feel they are alone.
She gives them love and guidance, and they all know her name--
They call her "Mother,"--she's a mother, just the same. (Chorus)

- - -
*When I'm feeling silly, I substitute "..don't leave the womb without one!"

Anyway, good luck gathering songs for your in-laws. (I wouldn't recommend the old song "Mother In Law!"--unless your in-laws have great senses of humor!)