Police and paramedics found the pair dead in their tent, and the child's mother needing urgent medical help, about eight kilometres south of the Wedge Island access road, some 150km north of Perth, on Monday morning.

Their pet dog also died.

The woman was flown to Perth in a serious condition, and a Fiona Stanley Hospital spokeswoman told AAP on Tuesday afternoon she had improved to a stable condition.

Police said the two deaths were not being treated as suspicious.

"Initial investigation at the scene suggests there may have been a fault with an item of camping equipment located inside the tent the family were sleeping in," police said in a statement.

Leslee Holmes, the president of the local Shire of Dandaragan, said a first responder saw a gas bottle outside the tent, which had its flaps up amid hot weather.

"It's just leaked in," Ms Holmes told AAP.

"People have mentioned a fridge - it may be the gas bottle that powered the fridge.

"Just how it's happened, I don't know."

Police Minister Michelle Roberts said she had been briefed the deaths involved a gas leak.

"It's a long weekend - so many people would have had a similar experience of camping in their tent, be it at Wedge Island or somewhere else, and they would have used potentially similar equipment," Ms Roberts told reporters.

Ms Holmes said the local community were all campers and boaties, so the tragedy had hit hard.

"Our whole community is rocked," she said.

The family was not supposed to be camping on the beach as it is part of an army firing range, but is "heavenly," Ms Holmes said.

"They where a long way from anywhere," she said.

Police are informing next of kin and a report will be prepared for the coroner.

Australian Associated Press