I really like how you made it all part of the story--that you are transferring a festival of Gondolin to Imladris and those weather and date issues! You've integrated it very cleverly with your vision of the early history of Imladris.
The twins make very believable children. I really got a feeling that they were at a particular age, at a particular stage of childhood.
I hope they discovered they enjoyed the dances! Elladan certainly has energy enough!