Birmingham have signed full-back Yan Valery on loan from Southampton and teenage forward Keyendrah Simmonds on a permanent deal from Manchester City.
Valery, 21, has joined the Blues until the end of the season while Simmonds, 19, has agreed a contract until 2023.
The duo join midfielder Rekeem Harper, who has joined on loan from West Brom, and striker Sam Cosgrove, a permanent switch from Aberdeen, as the Blues' additions in January.
Midfield pair Josh McEachran and David Davis both left St Andrew's earlier this month.