From Sydney Airport's page:
A family entering Australia can pool their individual allowances.
For example: a family of 4 (2 adults and 2 children) are entitled to
4.5 litres of alcoholic beverages (2 x adults alcohol allowance of 2.25L= 4.5L)
100 cigarettes (2 x adults tobacco allowance of 50 cigarettes = 100)
$2,700 worth of general goods (including gifts, souvenirs, cameras,
electronic equipment, leather goods, jewellery, watches and sporting
goods) (2 x adults general goods allowance + 2 x traveller under 18
years general goods allowance).
(edit) So to be clearer - for alcohol and cigarettes, you cannot allocate to the kids, but you can for other items with no age limits.