I'm not sure what's happened to Elliott and Brewster from this squad, they were originally named in the 23 man squad along with Jones and Williams and it was said they'll be travelling after the Villa game. But Jones and Williams are named here so assume they're not playing the League Cup game at all. Maybe this is just the players travelling today, I don't know.
On the point of first team players being left behind, I'm not sure how well it would have gone down if you told say, Milner, Lallana and Shaqiri 'we're going to go and become World champions but you're staying at home to play a League Cup quarter final'.
I agree that it's potentially not going to be good for the young players development though, I said as much when the situation became clear. I thought there would have been another solution that didn't involve us playing two games in less than 24 hours