In the Pali suttas, the word "a being" ("satta") refers to "a view" generated from "strong attachment", as follows:
Why now do you assume ‘a being’?
Mara, is that your speculative view?
This is a heap of sheer formations:
Here no being is found.
Just as, with an assemblage of parts,
The word ‘chariot’ is used,
So, when the aggregates exist,
There is the convention ‘a being.’
'A being,' lord. 'A being,' it's said. To what extent is one said to be 'a being'?
Any desire, passion, delight, or craving for form, Radha: when one is caught up there, tied up there, one is said to be 'a being.'
Any desire, passion, delight, or craving for feeling... perception... fabrications...
Any desire, passion, delight, or craving for consciousness, Radha: when one is caught up there, tied up there, one is said to be 'a being.'
Just as when boys or girls are playing with little sand castles: as long as they are not free from passion, desire, love, thirst, fever, & craving for those little sand castles, that's how long they have fun with those sand castles, enjoy them, treasure them, feel possessive of them.
MN 64 says a new born child has no "self-identity" therefore has no notion of "a being", as follows:
For a young tender infant lying prone does not even have the notion
‘identity,’ so how could identity view arise in him?
A young tender infant lying prone does not even have the notion
‘beings,’ so how could ill will towards beings arise in him?
MN 38 clearly explains it is only when a child reaches a certain age does the idea of "a being" or "a birth" arises in their mind, as follows:
The mother then carries the embryo in her womb for nine or ten months
with much anxiety, as a heavy burden. Then, at the end of nine or ten
months, the mother gives birth with much anxiety, as a heavy burden.
Then, when the child is born, she nourishes it with her own blood; for
the mother’s breast-milk is called blood in the Noble One’s
When he grows up and his faculties mature, the child plays at such
games as toy ploughs, tipcat, somersaults, toy windmills, toy
measures, toy carts, and a toy bow and arrow.
When he grows up and his faculties mature still further, the youth
enjoys himself provided and endowed with the five cords of sensual
pleasure, with forms cognizable by the eye… sounds cognizable by the
ear…odours cognizable by the nose… flavours cognizable by the
tongue…tangibles cognizable by the body that are wished for, desired,
agreeable and likeable, connected with sensual desire, and provocative
On seeing a form with the eye, he lusts after it if it is pleasing;
he dislikes it if it is unpleasing. He abides with mindfulness of the
body unestablished, with a limited mind, and he does not understand as
it actually is the deliverance of mind and deliverance by wisdom
wherein those evil unwholesome states cease without remainder. Engaged
as he is in favouring and opposing, whatever feeling he feels—whether
pleasant or painful or neither-painful-nor-pleasant—he delights in
that feeling, welcomes it, and remains holding to it. As he does so,
delight arises in him. Now delight in feelings is clinging. With his
clinging as condition, being comes to be; with being as condition,
birth; with birth as condition, ageing and death, sorrow, lamentation,
pain, grief, and despair come to be. Such is the origin of this whole
mass of suffering.
On hearing a sound with the ear… On smelling an odour with the
nose… On tasting a flavour with the tongue… On touching a tangible with
the body… On cognizing a mind-object with the mind, he lusts after it
if it is pleasing; he dislikes it if it is unpleasing…Now delight in
feelings is clinging. With his clinging as condition, being comes to
be; with being as condition, birth; with birth as condition, ageing
and death, sorrow, lamentation, pain, grief, and despair come to be.
Such is the origin of this whole mass of suffering.
It may be noted the eternalist translator of the above titles the above section as "The Continuation of the Round". But his title is obviously his own addition to the text & wrong. It should be titled "The Start/Commencement of the Round". Therefore, there is a time when a child has its first "birth"; its first mental conception of "a being" and "beings".
Also, it should be noted the word "birth" ("jati") means the birth of the view or conception of "beings", as follows:
And what is birth? Whatever birth, taking birth, descent,
coming-to-be, coming-forth, appearance [manifestation] of aggregates & acquisition of
[sense] media of the various beings in this or that group of beings,
that is called birth.
It should also be noted many will vomit up hot blood when their 'being' reads this answer.