There's nothing wrong with kids watching R rated, or even just "scary" movies.
My ex let her daughers watch Godzilla 2014, Cloverfield, The Exorcist, Alien, and Halloween.
Kids love that shit.
If you take away the R-Rated aspect of the Alien and Predator series and just look at the raw details, there's a lot there to exploit and market to kids. You have wonderful set pieces, cool monster designs, gadgets and gizmos. Ideal for playsets, figures, dress up.
About the time I saw the first ALIEN (On TV, brought you by Tylenol.) I also saw the movie "Spaced Invaders" which is a fun little b-movie, in it the little girl is actually wearing a home-made Alien costume for Haloween. I loved that as a kid. I wanted one.