I think it is very clear.The number of passengers carried in an aircraft for which an emergency evacuation demonstration is not required may exceed the number of approved passenger seats fitted in the aircraft only if the excess number of passengers:
(a) has been approved by CASA; or
(b) does not exceed the number specified in column 2 of the following table opposite the number of passenger seats specified in column 1; and the excess passengers are infants or children:
Column 1 is number of seats (2-6), Column 2 is number of EXCESS passengers (1)
SO IF YOU HAVE 2 SEATS YOU CAN HAVE 1 EXCESS PASSENGER as long as that passenger is a child