We know that through prescience Paul saw a female child (Ghanima can we assume) only because Leto II is an oracle more powerfull than him.
Also i remember that Alia in one of her spice overdoses saw a son, at first i tought that was Leto, not because it seemed to be Alia's son but because of the duality of Paul/Alia as like both make a prescient vision more perfect or accurate or maybe they work sometimes like a unity (i remember someting like that when Eldric visited Paul in DM), or maybe because Alias was very high on spice

So who was the child in her vision?
Leto? unlikely because the oracle thing
Her future son with Duncan Ghola?