Below are some links, and you may find a lot more on the web.
Dial an Angel
Tel: 9362 4225
Open 8.30am-8.30pm daily. Rates from $48 first three hours.
Offers nannying/babysitting service, 24 hours a day.
Sydney Nappy Wash
Tel: 1800 262 600 Open 9am-5pm Mon-Fri; 9am-noon Sat.
Sydney Nappy Wash costs $26-$28 per hour.