One limitation is that child items don't have SKUs or Listing IDs on Etsy. This makes it difficult for us to import them as individual products, or manage them independently, like we do with other marketplaces.
Also, quantities cannot be assigned to child items on Etsy. The quantity of the parent item applies to every child item in the variation. If you need to manage the quantity of child items individually, you need to list the items separately instead of as a variation.
Many sellers and developers have contacted Etsy about enhancing the way they manage variation listings. Hopefully they will make changes in the future.
In the meantime, we are currently working to develop a fresh approach for supporting Etsy variations.