Lara Jill Miller? Good choice. I always thought she was a doll.
Mine was Denise Huxtable from The Cosby Show. It became an eye-opening experience when I saw Lisa Bonet later in Angel Heart.
Susan Dey aka Laurie Partridge. Or maybe Jenny Agutter in Walkabout. Whichever came first.
Ditto, but I had a crush on her before she was married, even before she was in the beach movies. At a very young age I knew there was something different about her.
Sugar Kane in Some Like It Hot. Yes, I had the hots for Marilyn Monroe when I was four years old.
As a very 4 or 5 I really liked Linda Carter as wonder woman, but I wouldn’t call it a crush. So probably the first fictional girl I was old enough to have a thing for would be Kitty Pryde of X-men Comics.
Shadow Lass, from DC Comics Legion Of Superheroes.
The earliest I remember was Janice from the Muppets. Also April from Teenage Mutant Ninja Turtles.
Star of my first celebrity erotic dream.
Sadly I can’t remember any particular one at all. I do remember my older sister and I watched Emergency! in syndication together in the late 70s, she because she liked either Gage or DeSoto (probably the recently deceased Randolph Mantooth, I’m guessing) and myself because I liked the trucks.
Col. Wilma Deering (Erin Gray) and Princess Ardala (Pamela Hensley) from Buck Rogers gave me funny feelings when I was young. Which one I liked best tended to change from day to day depending on how I was feeling.
I’m rather surprised by the people who remember their first fictional crush. I couldn’t really say who was first for me, but there have been a lot of contenders mentioned in this thread so far.
I had as much of a chance with fictional crushes as I did with real life crushes until I hit 30.
I am not sure if Catwoman or Batwoman were my very first- but certainly I had a crush on them, and quite early.
Reading Bill Bryson The Life and Times of the Thunderbolt Kid: Travels Through My Childhood it seems it was Gloria Winters as Penny King in Sky King for him. 
I’ll admit that my choice of Emma Peel is an educated guess. Judy Robinson might be another candidate, but although I liked looking at her, she was just kinda “there” without doing much. Marlo Thomas as Ann Marie in That Girl caught my attention as well.
But Mrs. Peel certainly had a more profound and lasting impact.than the other two.
I’m fairly promiscuous with television character crushes anyway. I have a thing for Kitty Forman on That 70s Show.
My brother had a thing for Cissy of Family Affair. Besides Billie Jo Bradley, i also had liked Barbara Cooper from One Day at a Time and Andrea Nuvo from Arnie.
Early 80s, reruns of the Brady Bunch came on at 4pm every day. I had my first crush on Cindy Brady, but it quickly moved on to Jan.
A lot of 6yr old kids with crushes on 30yr old adults here. Wonder what that’s about.
Better than the other was around I’d say.
Many kids at that age can have a sort of romantic/emotional attraction or infatuation with others, including classmates and playmates as well as people who are older than them (teens and adults), both people they personally know, as well as celebrities on TV and movies. It’s not particularly unusual or strange.
I was in my early teens. Who here said they were six years old?