Happiny was released with the start of Valentine's Day event on February 13th, 2019.
Since April 26th, 2019, Happiny can be hatched from 7&10-km Eggs with a 212 of maximal CP.
From February 13th, 2019 to April 26th, 2019, Happiny used to be a possible hatchling from 7-km Eggs.
Between April 16th and April 23rd, 2019, Happiny was temporarily possible 2-km egg hatchling during the Eggstravaganza event.
Happiny was originally planned to learn Dazzling Gleam, but it was removed before Happiny was released. No new charged attack was compensated. As a result, Happiny now only has one charged attack. It is possible that Niantic does not want Trainers to unlock the second charged attack with Baby Pokémon discount since Chansey and Blissey are good Gym defenders which require more resources to unlock a new attack.