Hearts trio Jamie Walker, Jason Holt and David Smith have joined Raith Rovers on a short-term loan deal.
Last week, the teenagers all signed new contracts keeping them at Tynecastle until 2014.
And now they will compete for places at First Division level over the next month.
"It's part of their development," youth coach Darren Murray told the club website. "I think they have outgrown the Under 19s."
Rovers are managed by former Hearts coach John McGlynn, who borrowed midfielder Denis Prychynenko from Tynecastle earlier this month.
The Kirkcaldy side have struggled this season and sit ninth in the table on 12 points from 13 matches.
Striker Smith has made one first team appearance for Hearts as a substitute, while Holt and Walker play in midfield.
"John McGlynn will look after them," added Murray. "These lads now have to fight for their place, in a team that isn't picking up a great deal of results but I'm sure with John's coaching ability that will change.
"He now has three of the best young players in Scotland and we're hopeful for them.
"When they come back they can maybe push for a place in the first team squad."