Both players current deals were due to expire at the end of June.
Midfielder Stirk, a Wales Under-21 international, has been a regular for Blues Under-23s.
Highly regarded as a ball playing midfielder with a velvet touch who can also mix it competitively, the 19-year-old has on occasions captained Steve Spooner's side.
He received a First Team squad number at the season's start and was on the bench for the Carabao Cup tie at Portsmouth in August.
Stirk, from Tamworth, joined the Blues Academy system in 2010 and has been very instrumental for the Development Squad this season.
Reid, 19, a strong-running striker, joined Blues in the summer.
Formerly with Manchester United and Swansea City, he impressed during a short trial period to earn a professional deal.
He has come into his own in recent weeks when football was active, netting an impressive scoring streak which helped yield nine Under-23s goals this campaign.
Reid, who carries a powerful presence, has also been included in First Team squads this season after earning a senior squad number.