Jadon Sancho has made a name for himself at Borussia Dortmund after moving from Manchester City in 2017, while Chelsea's Callum Hudson-Odoi wanted a move to Bayern Munich in the January transfer window.
Barnes told Sky Sports: "I think it can be difficult for young players, a lot of time people don't realise what the gap is between U23s football and the Premier League, one of the best leagues in the world. It is a massive step.
"For me I felt like I had outgrown U23s football and needed that experience out on loan, so for me that was the route I needed to take. It has worked out so far.
"Other players will sort of progress from the U23s into the first team and make that natural step, but it's definitely as tough step to take.
"Of course there will be limited opportunities for young players, that's got to be expected, because even the senior players in the Premier League are never guaranteed to play. I think for a lot of young players, loans will really work out for them.
"For Sancho, he's got great opportunities out there, and you can see why the young lads are following that route, it puts them out on the pitch and showcases them as a player, which they might not get out here."