I would take the whole u19s squad, plus perhaps Sterling, Kane and Ali.
What is the point in taking a bang average squad, that inspires nobody whatsoever and yet again comes home from the group, or at best second round? Lets take a load of kids, at least then it will give us something to get excited about, whilst at the same time giving the future starts some vital experience.
There is absolutely no hope of this England squad doing anything different from the last 5 or 6 tournaments, so why not do something different? It will never happen though, because it would take a manager with something about them, which we don't have.
This is such an awful idea its amazing how often fans repeat it. The reason a manager would never do it is because no one with the ability to be a professional manager could possibly be so stupid.
Firstly, England are nowhere near so bad the team is "at best second round". Are you really telling me you can not even in a best case scenario see England defeating Poland, Senegal, Colombia, or Japan in a second round game?
Secondly, even if you took the under 19 side, people would not be favourable to them WHEN they did badly. When they invariably got knocked out at the group stage because they're still mainly kids with little first team experience, people, mainly the people who suggested such an idea in the first place will be the same ones slating them and endlessly going on about how overrated they are for losing to Tunisia.
Thirdly, you can't tell how they will even develop so its a waste to put all your eggs in one basket and hope they do. England have taken far more established young players to world cups who never pushed on. Look at the last world cup, 4 years on Shaw isn't remotely in contention, Barkley isn't in contention, Wilshere if he makes the squad in the first place looks like he'll only do so because of injury to Ox, Ox himself was pretty useless the 3 years after that world cup, Smalling won't even be part of the squad. Where exactly is the evidence that simply going to a world cup is so good for developing players? There's absolutely none. Doing well at a world cup maybe.
Fourthly, your plan involves writing off young players who've done nothing wrong for England anyway. Apparently Pickford, Lingard, Stones, RLC, Maguire etc are gone despite never playing in a tournament in the first place.
Finally, have you ever actually seen a team give up a world cup in favour of supposedly building for the next one? No you haven't. There's a reason. It's an utterly stupid idea that fans really need to stop parroting.