I just got to the part where Luffy arrived to Amazon Lily.
I started wondering, how do the women multiply in Amazon Lily as there are no men?
There were kids, so they must've some method.
Maybe you could explain?
Some of the resident leave Amazon Lily and sometimes, they come back pregnant.
They didn't bring their husband, because it's forbidden for men to enter Amazon Lily, but they still keep the baby and raise them inside the island. However, they always give birth to females. There's still no answer, but from a question about why all Kuja tribe born as a woman? and also from the picture above, it just happens mysteriously.
The Amazons (women who could fight like men) are warrior race from Greek mythology.
In One Piece, the Amazons are depicted as they are in the myth so they must be following the same methodologies to reproduce.
Here are some of the accepted ways of their reproduction.
Amazons met with men from nearby societies and chose suitable partners, would take them into the darkness of the forest and couple with. If they gave birth to a male, they were said to kill, blind or cripple the infant. If they kept them alive, they would then use them when they grew into young men (if they were suitable) as a supply of male seed. They also took men prisoners in battle. After choosing the most handsome, they then used them for their sexual pleasure, and would either kill them or use them as slaves once their usefulness had been expended.
Amazons reproduce by going into a nearby village and seducing the males one night every few months. If they had male babies they would send them downriver to the men and keep the females.
Hope this helps.
This is just my hunch, but it's said in anime that if anyone from Amazon Lily fell in love with a man, they have to leave the island. So it might have been the case that some women fell in love with men, had kids and then they brought their daughters with them to the island and left their husbands. Or it might also be possible that many women were adopted or allowed to live on the island by the Kuja Pirates.
You can see Nyan-ba staying on the island even though she fell in love with a man and was forced to leave the island before. Also it's explained that she brought Hancock and her sisters with her to the island.
This is just a hunch but I am satisfied with this. Hope you also agree.