I don't get why a 4 door STI isn't right for kids?
people buy 4 door civics for kids but an STI (bigger) isn't good enough.
your 06 is plenty fine for 2 kids, only issue would be having to move the seat forward to accomodate the second car seat.
but you could just strap that one in on the driver side and you'll know what it's like. 2 car seats in a 4 door 5 seat sedan is what the norm was 10 years ago. Most are too accustom to uber huge ****ty-van's or monster soccer mom suvs.
PS, ive had my kids car seat in my 10 STI and 09 FXT and it's fine. Trust me until you hit 3 kids the STI is perfect. ( I don't have 3 but I know you can't fit three across in car seats