Costs associated with second child

I'm a FTM with a 5 month old and I'm trying to figure out when to return to work. I have enough savings to be off for at least 12 months, but wondering if I need to return to work earlier as my husband and I are keen to have a second child (will likely try around 12 months).

How much does it cost to have a second child? I'm guessing I will need to factor in costs of a larger car, double pram, and another car seat.