Both players temporarily played for the Eredivisie side last term and have agreed another switch.
Kalas made 29 appearances for Vitesse over the course of the season and penned a contract extension with the Blues until 2017 before departing for the Netherlands.
The 19-year-old is joined at the club by Van Aanholt, who played nine games for the club last season having also spent time on loan at Wigan.
Source: PA
Source: PA