How to destroy random child actor component?

Hi, I am spawning a row of 7 rocks, after I spawn the row of 7 rocks I want to random destroy 1 rock which will leave a gap, I cannot figure out how I do this or if I can. I am using a child component because I am destroying the parent after a delay in which I want the child actors do be destroyed too.

I have gotten it to almost work but sometimes its spawning all rocks, last index is 6

I think that it is getting a random number for every loop pass it does, how can I get it to fetch one random number and use that for every loop pass