To convert your stroller into a tandem, you will require the tandem adaptors. The tandem adaptors allow you to double up in 6 approved configurations.
When using two infant car seats together in tandem mode, you will require lower multi car seat adaptors, to affix a car seat at the bottom. For the higher tandem position, you will also require the standard multi car seat adaptors. Click here to find approved car seats in tandem mode.