I’m aware that this question has been asked a thousand of times already, but this time I really haven’t found any answer to my question.
Is it:
We all had been a child once.
Or
We all have been a child once.
Thank you for your time.
I’m aware that this question has been asked a thousand of times already, but this time I really haven’t found any answer to my question.
Is it:
We all had been a child once.
Or
We all have been a child once.
Thank you for your time.
Both are very awkward.
You're separating the structures and masking the issue a little, but you don't have agreement on number, for starters.
Simplify it, bring it to simple present tense and you will see why.
We all are a child.
hmm… no. Try
We all are children.
Better.
So, let's take it back into past tense. The simplest version is the one most likely to be used in common speech.
We all were children once.
If we build from that, then we could use
We all have been children once, or
We all had been children once.
Both are now acceptable, but feel a little 'stiff'. Each could have its place, but you'd have to choose carefully. Stick with the simplest version.
The choice between 'all were' or 'were all' is stylistic. 'All were' still feels a little archaic, but actually is a form I use a lot. (I'm old ;)