"The granting of this determination means that Pfizer is now eligible to apply to vary the provisional approval for the vaccine to include children aged five to 11 years," the TGA said in a statement.
"This provisional determination is the first step in the process and does not mean that an application for variation has been made by the sponsor or that any such variation will be provisionally approved by the TGA."
Pfizer will now need to submit comprehensive clinical data.
Health Minister Greg Hunt said the assessment would be done "very quickly", potentially in a matter of weeks.
He said it would also need the green light from the technical advisory group ATAGI.
"It will be assessed very quickly," Mr Hunt told 4BC radio.
"We are hoping they (Pfizer) bring it forward in the coming weeks.
"We've got the supply and we've got the distribution mechanisms."
Pfizer said this week the company had provided trial data to the US regulator for initial review.
A trial of the two-dose vaccine involving 2268 children had come back with favourable safety and antibody responses.
The pharmaceutical giant is also running a study involving children aged six months up to five years, which should produce topline results by the end of this year.