Southgate, who also says he is keen to continue in his role, said the absences of Saido Berahino, John Stones and Luke Shaw had proved costly.
A knee injury kept Berahino out of England’s campaign, which culminated in a 3-1 loss to Italy, ensuring England finished bottom of their group. Stones played against Italy but missed the opening two games with concussion, the same injury which denied Southgate the services of Shaw.
“I think the regret is that, for the three games and the players that we wanted to select and had chosen to select, we didn’t have Luke and Saido, and not Stones until the last game,” he said.
“At senior level, if you lose three of your top players it has a big impact. At age-group level, it’s even more significant.
“That’s not to take away from the players that are here and have played and have given absolutely everything, but they’re three players who have been with the seniors and would have been key in our plans to attack the tournament.”
England finished their tournament with just two goals from 56 shots, a strike-rate that stands in stark contrast to the team’s prolific qualifying run.
“I think it’s pretty straightforward,” Southgate said of the tournament shooting statistic. “You would back the players that we’ve got to put those chances away as well.
“I think we’ve learned. This has been a step up for them in terms of the spotlight on them, the attention, the pressure that they will have felt.
“It’s not quite the exposure and the difficult situation that they would face with the seniors but it’s well on the way to that. They’ll know what’s coming when they go into a senior tournament and what they’ve got to cope with.
“Individual techniques of defending, in the end, for the goals against Italy have been costly, and the chances that we missed. But I think that for them, as a life experience, it’s invaluable. Absolutely invaluable.”
After discussions with England senior coach Roy Hodgson, Southgate chose a squad which excluded young stars Raheem Sterling, Jack Wilshere, Alex Oxlade-Chamberlain, Ross Barkley and Phil Jones.
But he refused to be drawn on whether the inclusion of those players would have made a difference, adding: “It is impossible to say whether we would have done better.”