Strictly within the context of Toys R Us, I don't see why they shouldn't stock adult products. I just checked the Toys R Us webstore and they stock GTA5, Assassin's Creed and CoD, so the idea that TRU is a "safe space" where children have no chance of being exposed to stuff for adults is already disproven. I'm guessing in the bricks-and-mortar store there's a separate "adult" or "collectors" section for figurines and self-assembly kits, so I doubt the Breaking Bad figures are literally being sold next to He-Man and Moshi Monsters.
In general though, I've always felt a little leery about the way adult franchises are marketed towards kids. When I was a kid, plenty of toystores and catalogues had action figures and play sets based on franchises like Batman, Robocop, Terminator, Nightmare on Elm Street, Chucky, Aliens and Predator. To be clear, this was long before the Batman animated series and the PG-12 versions of Robocop, Terminator and AvP - these were teen or adult franchises being squarely aimed at pre-teens. And that boggles my mind. When little Timmy wants to watch the movie his cool Robocop figure and car are based on, what are we supposed to tell him? "Sorry kid, you can't watch that movie because it depicts a guy falling into a vat of acid, partially melting, and being run over. Carry on having fun with your toys though!"