The Tottenham youngsters have flourished since joining the Robins in August, with defender Caulker being nominated for the npower Championship player of the month award in November.
"They both joined us on youth loans for the season. The only reason they would go back to Tottenham is if they are required in Harry Redknapp`s first team," Millen told City`s official website.
"We speak regularly with Tottenham about their progress and they spend a couple of days early in the week training with their parent club when possible.
"The main thing is they are both enjoying playing regular football here and they are not likely to get that at Spurs at the moment, so I see no reason why both won`t be here until the end of the season."
Source: PA
Source: PA