Their mortgage may be higher than what you are paying - everyone's is different as it will depend on how much they had to borrow. Their utilities will be different too depending on how energy efficient their house is and what type of heating/hot water system they have. It also depend on their providers for internet and mobile and what plans they are on. Another difference could be where they shop and the sort of food they eat, the type of nappies etc they use. All of these things can make a huge difference to your spend.

FWIW our weekly spend is about = $1600 for a family of 4 which includes mortgage, childcare, health ins, food, utilities, phone, internet, savings, rates, insurance, rego, spending money, petrol, public transport, gifts, dog food, education savings plan etc.