Aidan Denholm, Sean Docherty, Ryan Schiavone and Harris Spratt have all earned new deals up until the end of the 2021/22 campaign.
Spratt plays in goal, Docherty is a right-back, Denholm operates in midfield while Schiavone is a striker. They are all 17 years old.
Under-18s boss John Rankin hailed the work ethic of the quartet but called on them to take it up another level.
He told the Hearts website: “It’s been a tough year for them. The end of their first year and entire second year has been difficult for them because of Covid.
“The hard work they’ve put in, not just at the club but with their training programme at home, has been great so the contracts are merited.
“It’s great for them to get to this stage of the season and be rewarded for another year’s contract. They’re coming to the end of the U18s and will be regarded as adults and will play men’s football.
“It’ll get harder from hereon in, now more so than ever. It’s down to them to take the responsibility and go and make themselves professional players.
“I keep saying to them, when they get a chance to train with the first team, that it’s not a case of only being there for a couple of days; make sure you stay there.
“They need to put demands on themselves. It’s a great reward but it’s only the beginning. They’ve been on a great journey so far but they need to continue their hard work.
“This is the beginning of their professional journey and they need to step up and earn a place in the manger’s training group and squads going into games.”
Sporting director Joe Savage added: “It’s no secret that we want to develop young talent at Hearts and see them progress into the first team.
“These lads are on the right track and earning new contracts is a nice reward for them.
“They need to keep up the hard work and push on and impress in training and in games. If they do then I’m sure we’ll see them knocking on the door of the first team when the time is right.”