The Delta variant has shown a propensity to transmit amongst children "much more" than previous variants, Health Minister Brad Hazzard on Monday told a Budget Estimates hearing.

He said there are "serious issues" around children in the current outbreak, which began in mid-June.

More than 200 children under 10 tested positive over the weekend in NSW.

More than 2500 people under 20 have tested positive since the start of August.

The national immunisation advisory group is considering whether to recommend vaccinations for children aged 12 to 15.

That age group is likely to be vaccinated in the near future, which would be an important control strategy, Chief Health Officer Kerry Chant said.

And she is "very optimistic" that Australia will achieve high coverage rates when vaccinations do open up to children.

"I would anticipate that 12 to 15s will go quite quickly and the other younger children will have access to vaccine in the new year," Dr Chant said.

Premier Gladys Berejiklian confirmed on Monday that Sydney schools would not return in September, promising to give an update in the coming days on the plan to get students back in classrooms.

The ability to vaccinate children, plus the case numbers, will inform what the return to school looks like, Dr Chant said.

Much of the transmission to children is happening through the household, where Delta "invariably" reaches children once it's introduced.

The spread is aided by the fact that large, multi-generational families are often living under the one roof in western and southwest Sydney, where between 75 and 80 per cent of new cases are being detected.

There has also been a number of outbreaks in childcare centres.

Parents should keep children out of childcare unless it's "absolutely necessary", said the top doctor.

Dr Chant said the best way to protect children is to make sure those around them are all vaccinated.

While NSW has not gone as far as Victoria in closing play equipment, parents should avoid going at busy times and should avoid interacting with others at playgrounds, she said.

"Clearly with the duration of the lockdown we are very conscious that people live in apartments and don't have access to a lot of environments and so it is a balancing act," Dr Chant said.

"But we've been very clear. Parents and children should not be congregating in any of those areas."

Ventilation in schools and childcare centres will be key, and early educators will be encouraged to play outdoors, as summer approaches.

The rates of hospitalisation and ICU admission amongst kids are much less than in the older population, Deputy Chief Health Officer Marianne Gale told reporters on Monday.

Some children are in hospital if their family members are sick and cannot take care of them.

Children 12 and over who are Indigenous, have medical conditions, or live in a remote community are already eligible for Pfizer.

NSW Health is taking steps to allow those children to get the vaccine in state clinics.

Schools are likely to eventually be used to roll out vaccines, said Mr Hazzard, though that decision rests with the federal government.

Australian Associated Press