From the perspective of his wife its about her spirit becoming strong enough to re-build the world in a better way, but grappling with her own anger and desire for power.
The child just wants to live. but will protect Max if it can.
In Mad Max I his wife is a weak victim and she and the son die.
In Road Warrior she comes back as a fierce warrior woman to protect both herself and the children, Max doesn't recognise her and she dies on top of the tanker. He does save his son though, in the guise of the Feral Child.
In Thunderdrome the spirit of his wife is angry over her multiple deaths. She has grown in power again and now rules Bartertown, but her urge to power has made her tyrannical. Max doesn't recognise her and pisses her off. She banishes him. He meets the children and ends up saving them, again saving the spirit of his dead son. At the end his wife forgives him, but he has ruined Bartertown and she has to rebuild it.
She does recognise him though before the end:
In Fury Road his wife is Furiosa. She's still angry with him. Again they don't recognise each other. This time he manages to protect her and help her back into power,hopefully creating a less-evil society and repairing the damage he did to Bartertown. The child-spirit guides and protects Max but the only child in the film (Joe's baby) dies.
So Max has to keep going to the next reality to see if he can save both.