Fourth grade is probably too young to convert children to Team Dark, lol.
LOL I can usually tell which ones are already on Team Dark. Some of them want to write horror stories or stories where the main character ends up in the hospital. As long as they can keep them semi-realistic, I let them go for it. Except for the one year I had a little girl who, when working on a "Somebody... wanted... but... so... then..." summary of her story idea, had a character named "Mangle" who wanted to make the swim team, but she couldn't stop hurting other kids. Imagining Mangle as a budding young serial killer who couldn't control her impulses to drown her classmates in the pool, I was like, "So... are you saying Mangle's a bully? And she has to learn to be a better friend and not bully her teammates if she's going to be on the team?" I'm not sure if that was actually her intent or not, but that's what she went with LOL. She was a girl after my own heart - sweet and quiet on the outside, secretly dark and twisted on the inside LOL.
I try to coach mine through dialogue and they have no interest. Alas. Especially my feisty one, every time it's writing stamina, it's like pulling teeth. Meanwhile I'm like, "I would love it if someone said 'You have fifteen minutes, write about anything' to me."
Right?! Although I never liked being forced to write for fifteen minutes right there in the classroom. I've always written better when I'm by myself, on my own schedule.
By fourth grade, most of them do include dialogue, especially after I've modeled it for them and taught them about showing not telling, but some of their stories are like ALL dialogue... just characters talking back and forth without a lot of description or action in between.