The Heiress and I have three boys. We chose these middle names for them:
Jackman - my dad’s first name
Carnahan - my wife’s family name
Washington - after the first President, a hero of mine
And you…?
No kids of my own, but I met some parents at a baby shower a few weeks ago who gave their kid the middle name of “Danger.” 
Both girls have family names: my grandmother’s name for the oldest, and our two mother’s middle name (which is the same) for the younger one.
Man, clearly I should have done that!
My son’s middle name is my maiden name, which was still my last name when I had him - but it’s a common men’s first name, so it doesn’t sound weird or pretentious. I liked the idea of him having something of mine, since he has his father’s last name.
My daughter’s middle name is my brother’s first name. He’s my favorite brother and one of my heroes. Plus, I’ve just always loved the name, and it goes well with her first and last names. It’s a unisex name.
I have two daughters. The oldest has the middle name of Abigail which turned out to be very popular in the retro trend that has happened with names.
The youngest has the middle name of Corrine which we just liked and it went with her first and last names.
We announced early on that none of our children would be named after family members because we didn’t won’t to deal with the fallout.
James. Because it sounds good with Alex. Also, he can be AJ later if he wants.
We have twins, and both my wife and I are of Scottish descent. One’s middle name is Gunn, the other Douglas, the names of the clans from which we descend.
Both her first and middle come from dear grandparents.
Our son’s middle name is George, which is a pass down name for three or four generations in my husband’s family. For our daughter we chose Susannah, simply because we liked it.
My husband wanted biblical names (more for aesthetic than religious reasons). Also, Ruth is my mother’s name and Joseph is the name of a man who was very important to my husband when he was younger.
David: my middle name & my father’s first name.
Elizabeth: Grandmothers’ name (both sides) and, frankly, I’ve always liked it.
Mallory: My ex-wife’s (kid’s mother) maiden name, for her father (who’s first & middle names are hated by him).
So: covering the family names, I guess, but I also like the simple sound of them.
Because I wanted family names:
Lane - maternal grandfather’s middle name
Jeanne - a variation of her dad’s middle name (Eugene)
Eugene - dad’s middle name
Charles - maternal great-grandfather’s middle name
Wilson after my husband’s musical hero, Brian Wilson. If he’d had a little brother, we would have used Richards, after my musical hero, Keith Richards.
For both of my kids, I gave 2 middle names. I liked the way the names sounded. With my daughter, the reason she got a 2nd middle name is that her first name and first middle name are after her father and his brother – while both are also acceptable girl names, they’re also fairly common so she got her own name, the second middle one. With my son, well…kind of similar story. Husband wanted him named one thing, which is far too common a name and so we needed a first name that sounded good with it, and the name I wanted to name my son turned into his second middle name. Oddly enough, he chose to go by that name when he started kindergarten.
My daughter’s middle name is Rose as we both liked it and it sounded especially pretty with her very uncommon first name.
My son’s middle name is for my late Brother-In-Law who I really loved and admired. He was 20 years older than me and 9 years older than my sister and he was a great and beloved man and teacher. He died far too young when I was only 15. I thought it was the right thing to do and my wife agreed.
What a coincidence, we also chose three middle names for our sons.
Oh, wait, you meant one for each child.
As it happens, in this part of the Netherlands it is very common to have three middle names, and everyone in my family but me does have three. It is so common that all official forms have a space to fill in your three middle names. I occasionally encounter someone here who does not believe me when I say that I only have the measly one. I just tell them I am a foundling.
Dearly Beloved came up with the names for our future children – four names each – on our fourth date. (He wasted one name as he expected Thing Two to be a girl, but when it became apparent that the name Elke would not do, Eldest solved the problem by naming his just-born brother).
In my ignorance I thought coming up with four names each for two children was quite something – until somebody told me that he had simply followed the local naming conventions in choosing middle names and proceeded to tell me (just from their names) a host of information about our family, including which of my children was older, that the eldest was also the first child born in his generation, and that we were Catholic.
However, giving your children four Dutch names each does cause some consternation in an American hospital and requires you to be both very firm and in our case required Dearly Beloved’s presence in the office where they fill out the paperwork for the birth certificate where he was required to actually type in the names because they couldn’t believe you would actually spell something like that. They are all traditional Dutch names but Dutch has a gracious plenty of vowels and tosses in the most unlikely combinations of consonants which can be disconcerting.
It was a shame that he was not called upon to type it in for Youngest, actually, as a typographical error in Youngest’s birth certificate resulted in Youngest being registered as a member of a Dutch noble family, which caused so much consternation on this side of the Atlantic that I ended up with a nice letter from the Queen (no kidding) clarifying that Youngest was in no way noble. Which we actually already knew, ahem but it is good to have these things clarified.
Whoops, I wandered again. We chose our kids’ three middle names according to the naming traditions of this part of Holland.
My daughter’s middle name is Paige.
Short version of why: To honor the person who’s probably most responsible for us deciding to have a kid.
Long version of why: A tale I haven’t told to many people, and probably won’t anytime soon.
Not a parent and not likely to be in this lifetime, but mine was chosen as a nod to my maternal grandmother.
My first name is Wendy (no family baggage), and my middle name is Kay, meant to be a diminuative of Katherina, which has been in my mom’s family forever. I should have been the next Katherina, but my parents didn’t want to stick me with one of my other grandmother’s names, which are just awful, so the Kay is our dirty little secret.
I don’t have kids, but my brother’s middle name is our father’s name. This tradition of son getting pop’s name as his middle goes back a few generations.
My middle name is my grandma’s on my father’s side first name. It’s Dorothy, which I don’t like much. My mom wanted to name me Daria, and I think that would have been an excellent compromise for Pop to allow that as the middle name–it would honor Grandma and give my Mom a say.