In the final analysis I think we have to accept that this [i.e., Malebranche's odd account of the linkage between the mother's brain and the brain of the fetus] is one of those occasions on which Malebranche abandons philosophical rationalism for dogmatic theology. He is looking for an explanation of the transmission of original sin, and thinks that this widely accepted theory of the maternal imagination provides it. If the growing foetus shares its mother's thoughts and passions, it partakes in her fallen state. It is indeed an enfant de colere, born to sin and - without the sacrament of baptism - bound for the flames of hell.
Now, it's true that Malebranche's motivations are theological here, and that the result isn't successful at all. But the last sentence betrays, I think, a misunderstanding of what original sin is. Original sin isn't actual sin, so Catholic doctrine is usually that it doesn't merit positive punishment; it is, however, a state of disorder in which a person is lacking what would merit the positive reward of meeting God 'face-to-face' in heaven. That is, original sin is punished - it falls under God's wrath - in the sense that those who die with original sin (assuming God yields no special mercy to them, which Catholic doctrine does not rule out, assuming that they are not cleansed of original sin by martyrdom like the Holy Innocents killed by Herod, and assuming they are not cleansed of original sin in response to their parent's desire to baptize them or to the prayers of the Church) will never have the Beatific Vision, and therefore never have perfect, supernatural happiness. They are not 'bound for the flames of hell'.
What this means is this. We've all gone through life, and we've had good times and we've had bad times. Some of our good times have been really good, and in those good times we have been genuinely happy. However, our happiness in those good times is limited, imperfect, and purely natural. The punishment of infants is that they can never be happier than you or I have ever been or (assuming God doesn't give us special graces) ever will be in this life. That is all. The hell of those who die with only original sin is to live our sort of life forever, and never have anything better. We keep forgetting that 'hell' (i.e., 'hades' or 'sheol') just means 'place of the shades of the dead', and so we incorrectly treat 'hell' as if it always meant 'hell of the damned' whenever it is used.
Dante in his Inferno extends this to the great philosophers and poets who weren't Christian. To see the truth is the highest happiness, and they have all done so to the highest degree human nature alone can. This is all they will ever be able to achieve. The same principle is at work: the philosophers and poets are in the hell of limbo, not the hell of the damned. This hell of limbo is not a particularly bad situation in which to find oneself; the highest part of it is called 'the limbo of the Patriarchs' since the Jewish Patriarchs (Abraham, Moses, the Prophets) waited there for the coming of Christ. What distinguishes the limbo of the Patriarchs from the limbo of the children is just that the Patriarchs, because they foreshadowed Christ, did not have absence of glory but only delay of glory as their punishment for original sin. Limbo isn't glorious either, but one could do much worse.
Aquinas discusses this all in his commentary on the Sentences, and it was summarized after his death in the 69th question of the Supplement to the Third Part of the Summa Theologiae. Nor can I think of anything in Malebranche that would suggest that he departs from this standard view. Pyle (like, alas, too many Malebranche scholars too often) is not really taking the trouble to understand Malebranche's perspective, but is content with occasionally scoring cheap (and apparently inaccurate) rhetorical points off of him.