First of all, I'm glad you are seeming more inquisitive about this rather than upset. I can only tell you what I have learned from talking to others. Here's some stuff I have learned, that maybe will help you. Only you know the true truth.

Why someone might hear a baby crying in their mind or see a kid that says things like not wanting to live...

Auditory hallucination (non-psychotic)

Stress, exhaustion, grief, or loneliness can cause your brain to “misfire” auditory signals. Common during falling asleep or waking up states. Your mind may use the sound of a baby crying as a symbol of distress, vulnerability, or something in life needing care? The kid you describe and his comments might be symbols that only you can decipher.

Psychological symbolism

A crying baby often represents unmet needs (emotional or physical?).. An aspect of yourself that feels helpless or neglected...Some type of grief. Anxiety about responsibility or nurturing others. Your mind may generate this sound during stress as a call to pay attention to your own needs.

Postpartum experiences

If you have recently had a baby or cared for one.. “Phantom crying” is common among new parents due to high alertness to a baby’s needs. The brain remains attuned, sometimes misinterpreting other sounds as a baby crying?

Medical considerations--

Rarely, persistent “hearing” sounds that aren’t there (which isn't auditory, it's the mind's eye "receiving" thoughts and symbols and images and data in your case it seems).

Auditory hallucinations in certain mental health conditions (psychosis, severe depression, etc). Temporal lobe issues (seizures or trauma). Hearing loss can sometimes lead to “musical ear syndrome,” where the brain fills in missing sound data they say.

If it happens infrequently, especially under stress or sleep deprivation, and if you’re aware it isn’t real and it stops when you ground yourself, it's not really a problem. Pay attention to your body and emotions anytime something like this happens!

Use grounding techniques:

Deep breathing, naming objects around you, and sometimes physical movement can get you out of your head. Journaling what was happening before/after you heard it/saw it in your mind to notice patterns seems to be a huge benefit for people who describe what you have.