They gave a preview for a 2 episode storyline that will air starting december 7th in japan. story involves Ash, Chloe, Goh and a returning Dawn getting involved with a battle between Dialga (the pokemon god of time) and Palkia (the pokemon god of space). so they encounter alternate universe selves, another dimension, etc.
The preview trailer shows to what appears to be ar. It looks like Pikachu gets turned into a pichu (its pre-evolution baby stage) and 4 pokemon become eggs (we dont know which. But likely Grookey, Piplup and Eeevee).
But Goh, Dawn and Chloe (plus their alternate selves) get turned into kids
https://www.youtube.com/watch?v=a1kyh9mbqA4