Liverpool's stars Henderson, Alexander-Anold and Oxlade-Chamberlain also made the list with Man City's John Stones and Raheem Sterling getting mentions in the 27-man squad.
Southgate said Maddison, who was out until the early hours of the morning before England's 2-1 loss in the Czech Republic, learned a valuable lesson about the increased spotlight surrounding the player and vowed to speak to him ahead of the upcoming games.
Oxlade-Chamberlain, who suffered a serious knee injury last season, has scored four goals in his last four games for Liverpool, including Tuesday's victor to beat Genk 2-1 in the Champions League.
The Three Lions host Montenegro on November 14 - which will be England's 1,000th worldwide - before travelling to Pristina three days later, with Southgate's side needing just one point to secure their place at Euro 2020.
The Chelsea youngster was called up to the England Under-21 squad last month following his return from an Achilles injury. They then travel to Kosovo three days later.
Southgate said Kyle Walker's worldwide career was not over despite omitting the Manchester City defender for a third successive squad, with Kieran Trippier and Trent Alexander-Arnold the preferred options at right-back. (Trent's) form for Liverpool has been really exceptional.
There is no room for Aston Villa midfielder Jack Grealish, while Tottenham's Dele Alli and Manchester United's Jesse Lingard have failed to win back their places.
England lead Group A with 15 points and need one more point to secure their place at Euro 2020.
"It's an opportunity for us to qualify for a European Championship which is a very important moment for us", Southgate added. As a manager you get a real feel for the history and privilege of leading the team.