Almost a quarter of WA children under 10 are now overweight or obese, with children in Perth putting on the most weight.
A special report, to be released today by the Australian Institute of Health and Welfare on key childhood health indicators, shows WA children are now among the fattest in the country.
Much of that extra weight is being put on by children aged between five and seven.
The institute reported that in 2007-08 just under 22 per cent of children in this age group were overweight or obese.
Four years later this proportion had grown to 24.4 per cent.
Among children aged between 10 and 14 the percentage considered overweight or obese had climbed slightly to 28.4 per cent from 28 per cent.
Boys have put on the most weight, with more than 27 per cent of all WA male children now carrying too many kilograms.
The proportion of girls overweight or obese has actually fallen to 25.6 per cent.
Over recent years, the proportion of non-Australian-born children considered overweight has spiked, jumping five percentage points to almost a quarter.
But locally born children remain the heaviest at almost 27 per cent.
Perth-based children have also put on more weight than their country cousins. Four years ago, just under a quarter of Perth children were overweight or obese compared with almost 26 per cent outside the city.
Now the proportion of children with unwanted kilograms in Perth is higher than in country areas of the State. Only children living in Sydney are fatter than Perth children. While losing the battle of the bulge, WA children are doing better in other areas.
Literacy and numeracy rates have improved, for both boys and girls and among indigenous and non-indigenous children.
Teenage pregnancy rates, while still above the national average, have also fallen, dropping more than 20 per cent between 2006 and 2010 among the indigenous population. Institute spokesman Fadwa al-Yaman said there were positives to be taken from the overall report.
Most Year 5 students were at or above the national minimum standard for reading and numeracy with measureable increases between 2008 and last year.
"The information released today shows good news in that infant deaths continued to decline between 2006 and 2012 from 4.7 to 3.3 per 1000 live births," Dr al-Yaman said. But there were also areas where measures showed a decline.
Indigenous mothers were more than four times as likely as non-indigenous mothers to smoke during the first 20 weeks of pregnancy.
Child deaths from injuries were three times as high in outer regional and remote areas compared with major cities.