Speaking after national cabinet met on Thursday, the PM insisted schools should not delay the start of the year until after the projected peak of COVID cases, as has been done in Queensland and South Australia.
While the cabinet did not make any specific agreements on how the return to school would look, a number of key principles were endorsed, including that schools are essential and "should be first to open and last to close".
"If schools don't open, that can add an additional five per cent to the absenteeism in the workforce," Mr Morrison said.
"It is absolutely essential for schools to go back safely and remain safely open if we are not going to see any further exacerbation of the workforce challenges we are currently facing."
Regarding Queensland and SA's decision to delay reopening schools by two weeks, Mr Morrison said children of essential workers would still be sent to school to ease the workforce burden.
"They are still addressing the key workforce needs and we hope they are getting as best possible education for the children of those essential workers when they go back," he said.
He said a detailed operational plan detailing the return to school was being worked through by states and territories and would be available next week.
Meanwhile, more than 140,000 children aged between five and 11 have been jabbed in the first three days of becoming eligible, including 55,570 on Wednesday alone, according to Health Minister Greg Hunt.
Opposition Leader Anthony Albanese said the federal government needed to provide assurances schools would be safe to allay the fears of anxious parents.
"Australians are voting with their feet, literally, staying at home. They are making their own decisions and parents will make decisions in the interests of their children," he told ABC News on Thursday.
"It is extraordinary that in the third year of the pandemic we have people getting their booster shot appointments deferred, we have children who can't get their first shot causing anxiety for parents."
Epidemiologist Catherine Bennett said while the Delta outbreak had caused more infections in children than before, adults were leading the tally with Omicron - particularly Australians in their 20s and 30s.
"Kids aren't more likely to get infected (and) if they are it's likely to be at home," she told the ABC.
"But most importantly rolling out boosters for adults at the moment as well as vaccines for children themselves will certainly make a big difference."
The Australian Education Union had expressed concern about how schools will go back, with President Correna Haythorpe saying schools could become quite significant super-spreader environments.
Ms Haythorpe also called for priority access for teachers to rapid antigen and PCR tests so they would be able to test themselves quickly and conveniently.
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