That they aren’t exactly children’s books 
But it’s what I read when I was a kid.
The bear in king of the grizzles
I really wanted to be Pippi Longstocking. She had the neatest stuff, was super-strong, had a bag full of gold, and no grown-ups around to tell her what to do.
And she had a horse, and a monkey!
I still want a Chinese apothecary cabinet like hers. Dozens of small drawers, each filled with treasure!
Pippi had it made.
My parents wouldn’t let me have a dog. I remember having had a very detailed fantasy in which I raised Old Yeller, fed him, groomed him, and played with him. And, of course, kept him from being shot.
It’s no accident that the best dog I’ve ever had (and still have) is Fozzie Bear, a big yellow dog who looks a lot like you-know-who.
Let’s see…I wanted to be Alec from the Black Stallion or Trixie Belden (or maybe Honey - she was rich). I wanted to be the kid from My Side of the Mountain - lived on his own in a hollowed out tree and hunted with a peregrine. I wanted to be Julie of the Wolves. I wanted to be Jane Eyre (without all that lovey stuff).
StG
I didn’t want to be any of the kids from the Trixie Belden books, but I wanted to live near them and be part of the Bob-Whites of the Glen. They always seemed to have so much fun together, and really care about each other.
I also desperately wanted to be the Fourth Investigator (okay, they’d have to change their name!) or, barring that, have a secret clubhouse buried in junk in my backyard.
These days I’m not a kid anymore, but I would dearly love to be a Hogwarts student and go through the whole magical-education experience.
Ha, I always liked them, but deep down, I wanted their stuff, the cool clubhouse in the old gatehouse, the spiffy Bob-White jackets, and the open access to a stable full horses. My goodness, I was a covetous little tyke.
I am ashamed to say it, but I used to wish I were one of the kids in the Happy Hollisters series. My home life was very unpleasant, and the Hollister family looked mighty fine to me. I also fantasized about being one of the girls in Little Women. Mostly I wanted to be Jo, but every now and then I thought of myself as Beth.
Not a movie (although Disney cobbled one together), but I seriously wanted to be Zorro (the Guy Williams one, of course).
I wanted to meet Hans Christian Andersen.
I thought my brother and I should be the kids from Escape to Witch Mountain. I see I’m not the only fan of that movie. I guess it was our generation’s version of Harry Potter escapism. “I’m not really a helpless child trapped in a miserable family, I’m really a powerful magical being.” If only.
Damn, I came in here to say I wanted to be Tia from Escape to Witch Mountain too! Or Jodie Foster as anyone. Or Trixie Belden. Or George, Nancy Drew’s tomboy friend.
Hell, I still want to be Jodie Foster. Or her friend. 
I was absolutely going to marry Atreyu. And also be just like him at the same time. The kid who played him in the movie was my first crush.
When I got older I wanted to marry Mad Martigan too.
TV, not movie (we didn’t see go to the theatre much as kids: 4 children, 70’s era–things were tough).
I had a crush on Holly, from Land Of The Lost.
I wanted to be Wonder Woman. I remember spending a lot of time twirling around the living room when her show was on.
I would have loved to be friends with Pippi Longstocking. No parents around, no rules, no one to tell me I had to stop playing and go home. 
I had really in depth fantasies about being one of the boxcar children when I was little. I also wanted to be friends with Ralph S. Mouse. I loved the idea of a tiny mouse riding a motorcycle!
One of the children in the Narnia stories. Or the kids in the Swallows and Amazons books.
I wanted to meet Reepicheep, myself. For much the same reasons that Skald suggests wanting to meet Rikki-Tikki-Tavi, but even better, because Reepicheep can talk!
I was going to say that, or Atreyu! Or a slightly older Atreyu could be my special someone…
Ponch & John from CHiPs
The Dukes from Dukes of Hazzard
Starbuck from Battlestar Galactica (1979)
Cylons from Battlestar Galactice (1979)
Everyone from Star Wars
Kirk & Spock from Star Trek
BJ McKay from BJ & The Bear
Johnny Sokko & his Giant Robot
Everyone from G.I. Joe
The Avengers from Marvel Comics
Speed Racer
T.J. Hooker