THE high cost of childcare is believed to be a key reason parents in Sydney's south-west are more likely to send their children to school at a younger age than those in the more affluent northern suburbs.
Kindergarten classes in south-western Sydney have twice as many children under five than those in northern Sydney, enrolment figures from the Department of Education and Communities show.
Only 1.8 per cent of kindergarten students in the northern Sydney region were aged four in July 2012, compared with 4.3 per cent in south-western Sydney. In the Sydney region, which takes in parts of the inner city, the eastern suburbs and the southern suburbs, the figure was 2.9 per cent, while the western Sydney region was 3 per cent.
By contrast, there are far more six-year-olds in kindergarten classes in northern Sydney than other regions, as parents delay sending their children to primary school.
About 20 per cent of kindergarten students in the northern Sydney region were aged six or older last July, double the proportion of students in the south-west.
In western Sydney, the rate was a little more than 15 per cent.
The Federation of Parents and Citizens' Associations of NSW says a lack of affordable childcare could force some parents to send their child to primary school early. Data from the 2011 census shows the median weekly household income in south-west Sydney is $1171. In the north Sydney and Hornsby area it is $2111.
''I would suggest that sometimes it's about access to quality childcare and, if you don't have access to that, then the option is to put your child into school,'' the federation's spokeswoman, Rachael Sowden, said.
In western Sydney, where David Galea is the principal of Doonside Public School, kindergarten students are also typically younger than their peers in the northern suburbs.
He agreed high costs could put childcare out of reach of many low-income families.
''There would be some parents who simply could not afford [to send their child to preschool],'' he said.
But he doesn't think his younger students are disadvantaged.
''When we look at a child's assessments in year 6 … very rarely does it matter whether they started younger or older,'' he said.
The convener of the Northern Sydney Regional Council of P&C Associations, David Hope, thinks the flexibility offered by long day care could also play a part.
''If both parents are working and want to pick their child up at 5 o'clock, well, unless the school has an after-school care centre, it's just one other hassle,'' he said.