[Grammar] Which part of speech is 'all' in the sentence?

[learning54]

Hi teachers,
Which part of speech is 'all' in the following sentence? Is it an adverb? If that is so, could you tell me a synonym?
Theyare all five years old.

Thanks in advance

 

[BobSmith]

[AmE - not a teacher]

each one? Not sure if it works or not:

They are each one five years old.

perhaps I'm just hearing it as:

They are, each one, five years old.

 

[learning54]

Hi Bob,
Thank you for your reply.

Best,
L54

 

[BobSmith]

I'm sorry no teacher was able to respond.

 

[learning54]

I'm sorry no teacher was able to respond.

Hi Bob,
Thank you for your concern. But someone has already told me what it is.
'All' is not an adverb, it is a determiner that takes the same location as an adverb in such sentences when it postmodifies.
They are all, each and every one of them, five years old. (Very similar if not the same as the one you wrote.):-D

Best,
L54