Manchester United legend Wayne Rooney has sent a 'proud' message to son Kai after the 16-year-old made his Old Trafford debut on Friday night. The younger Rooney came off the bench during United Under-18s' FA Cup fourth round win over Derby with his mother and father watching on in the stands. Darren Fletcher's side had to work hard to claim victory on home turf, however.Derby took the tie to extra time having played out a 0-0 draw at Old Trafford. United, though, broke the deadlock shortly before the break in the additional period as defender Luca Crolla inadvertently turned James Overy's ball into the box into his own net.And United doubled their advantage two minutes after going in front as Chido Obi all-but sealed his side's spot in the next round of the competition. Max Nessling struck in the 113th minute to set up a nervy finish, but United held out to set up a last-16 meeting with Oxford.However, the standout moment of the night came when Kai Rooney was introduced to chants of 'Rooney! Rooney!' from the stands. The 16-year-old caught the eye during a bright cameo off the bench with Wayne and Coleen watching on in the directors' box.And the elder Rooney took to X to express how 'proud' he was of his son for making his first appearance at the Theatre of Dreams. The post included an image of Kai walking out with his father at Old Trafford when the latter was still a player, and another of the former in action against Derby with the message: "Then and now. Proud of you Kai."It was one of the rare times that Rooney has been able to watch his son live in action. Wife Coleen has previously explained that Wayne was prohibited from attending Kai's early matches in order to allow their son to play without the added distraction of the ex-frontman being in attendance. "How do you say to all of these kids: 'Go away, I’m watching my son?' Adults, it’s different, you could speak to them, so he just said: 'Oh, dad there’s no point you coming because you don’t even watch me play anyway'," Coleen revealed on I’m a Celebrity…Get Me Out of Here' in 2024.Rooney moved to United from Everton in 2004, and spent 13 years on the club's books before returning to Goodison Park in 2017. The former frontman is United's club-record goal-scorer having struck 253 times during a trophy-laden spell in Manchester.In his time with United, Rooney won the Premier League five times, the Champions League once, the Europa League once and the FA Cup once. And the ex-England star will hope son Kai can follow in his footsteps with the Manchester giants.Looking for smarter football bets? Get expert previews, data-driven predictions & winning insights with GOAL Tips on Telegram. Join our growing community now!Rooney wasn't the only notable United face in attendance at Old Trafford on Friday night. Indeed, director of football Jason Wilcox, director of recruitment Christopher Vivell and academy director Stephen Torpey also watched as United U18s beat Derby.United boss Michael Carrick also watched the U18s in action ahead of Sunday's trip to Arsenal. Carrick returned to the Old Trafford dugout last week having succeeded Ruben Amorim as head coach following Fletcher's promotion to first-team interim.The former Middlesbrough boss, who briefly took caretaker charge for the Manchester side in 2021, oversaw a 2-0 win over rivals Manchester City last weekend as United made a winning start to life back under his management.And having hampered one title rival, United will hope Carrick can repeat the feat when they take on Arsenal at the Emirates on Sunday afternoon. Add GOAL.com as a preferred source on Google to see more of our reportingArsenal are currently seven points clear at the top of the Premier League table, but have failed to win their last two league outings having been held to successive draws by Liverpool and Nottingham Forest.However, both City and Aston Villa have also dropped points in recent weeks, which has enabled the Gunners to extend their lead at the summit.