As with many other times, Kilta, I feel you simply don't know what you're talking about.

"Giving birth to 1 child at a time" and "renting 3 movies at a time" are the same meaning.

They imply that once you are done with the 1 child or the 3 movies, you can have 1 or 3 more. Same with leves.

Leves apparently have a gestation period of up to 36 hours, but no one tells you this so it would be safe to assume based on the phrasing that you could turn in 8 leves and pick up more. Similar to how you can only have 16 Quests active "at a time" but once you finish one, you can start another one. No need to wait any amount of time.

You can just accept that you and the NPC are both inaccurate. This is the last time I'll say so.