Now that Ben Affleck has been cast as Batman (which i'm completely fine with) we know that they're going with an older already established Batman. And, since this universes Batman will be more in line with his comic counter part, a Robin(s) shouldn't be too crazy of an idea. Batman will be about 40 years old so one or two robins would would be acceptable. I would love to see Bruce Wayne roll into Metropolis with Dick Grayson and Tim Drake already established in their roles as Bruces' adopted children and Nightwing/Robin.
Who do you think should play them? I think Tyler Hoechlin whould be a great Dick Grayson. He's 25 years old and has the build. Tim Drake could be played by....Kit Harrington, maybe? He's actually 26 years old but he's physically smaller than anyone here (5'10 and skinnier build) and he looks young.
The good thing about having Robins established is that they could pull of a 'battle for the cowl' movie version if Ben Affleck ever fills like the role is becoming to physically daunting for him. Imagine Nightwing taking over for Batman with a little Damien Wayne as Bruce Wayne sits back and controls surveys from the Batcave. That would be awesome! And it would work in film because the audience would be used to the characters