I'm kind of with you on that. I mean I will admit that sometimes kids have subconscious feelings that they act out in play. That's possible that they sensed something.
But I do not believe it is likely they were abused prior to the murders, or that he was practicing on them. And kids do odd things all the time. Then sometimes parents post those things because they seem so bizarre.
There are whole Rediit threads about creepy things little kids have said or done. Like:
"I was tucking in my two year old. He said "Good bye dad." I said, "No, we say good night." He said "I know. But this time its good bye."
Had to check on him a few times to make sure he was still there."
"Daddy sleep" then pushing my head underwater at the pool."
"I jokingly asked: "What's the best way to get a girlfriend?"
7-year-old's response: "Tell her to be my girlfriend or she'll never see her parents again."
"I work in a preschool. Creepy **** gets said and done all the time. The one that sticks out to me happened last year. There is a small kitchenette area in our classroom that the kids use during free time for playing house or whatever pretend games they think up. There was one little girl that I was keeping a close eye on, mostly because of how withdrawn from the other kids she was. I noticed she was playing with a babydoll in the kitchenette, rocking it back and forth and singing to it.
She then took the baby, shoved it into the play oven and slammed the door shut. She turned around, looked straight at me, and said, "Sometimes bad babies go in timeout" in the creepiest little girl voice I've ever heard before smiling and running off. That one kind of shook me."
The thing is, it's the coincidence and timing of this photo that's creeping people out. Hard to not see something sinister in retrospect. But my feeling is it is likely just a coincidence.