Depends on how snake they are. If it’s the typical 50% Lamia then the babies would be in the lower abdomen (like humans) but the vagina would be snake-like (A horizontal opening covered by scales) with their “legs” being pure muscle. But, if they’re the 70-90% Lamia then their vagina/womb would be near the end of their tail.

Though in both cases it’d come out the snake part.