Children could be left to "roam the streets" because of a shortage of after-school care in Perth, the WA Primary Principals Association has warned.
Demand for before and after-school care is rocketing, prompting calls for more on-site services at primary schools.
Only a fifth of WA State schools offer out-of-hours care centres, which are privately operated, meaning some parents have to hire nannies or babysitters, often at extra cost.
The WA Primary Principals Association is lobbying for newly built schools to have day care and after-school care centres on site.
"Every week we hear a story about the inability of working families to find appropriate care for before and after school," president Stephen Breen said. "There is huge demand. I don't think bureaucracy or governments have kept up with the pace of modern society."
There are fears demand will explode when Year 7s move to high schools from next year, leaving parents to seek alternative care arrangements or leave their children unattended.
"Parents need their jobs, so, yes, I would expect 11 and 12-year-olds would either be at home or some roaming," Mr Breen said.
"Kids are going to get into trouble. They need to be occupied in meaningful recreation. But there's no choice for parents."
Dial-an-Angel manager Kate Spencer said demand for nannies and babysitters before and after school had increased dramatically and the agency had been inundated with inquiries for the coming school year.
"Five years ago I can't recall it being an issue but over the last 18 months to two years we've had a significant increase in the amount of inquiries," Mrs Spencer said.
"The increase in shiftwork and the change in working hours, which used to be 8.30 to 5, has contributed.
"People also used to have a lot more help with families until recently, but now a lot of grandparents are continuing to work."
The WA OSHClub branch runs 60 programs in WA schools, up from just four in 2009. Team leader Robyn Johnston said requests from WA primary school principals and school communities for care to be housed within schools were growing.
"Demands are in all areas, southern and northern suburbs," Ms Johnston said.
Department of Education executive director of early childhood education Garry Hewitt said there were 323 approved OSHC centres in WA, more than 130 of which were on public school sites.
"The department supports public schools to enter into agreements so third-party providers can run outside school hours care services at schools," Mr Hewitt said.