This happened between Revalation and Humanity in the YJ universe. And the lucky duo still doesn't have the identity reveal.
Chapter 1: A Lucky Introduction
/Mt. Justice/
/October 4/
They were called by Batman to gather for debriefing. A few days after the Injustice League's giant plants fiasco, the team planned to spend a movie night together after training with Black Canary.
Once they gather in their uniforms they saw two middle school aged teenagers standing between the Black Canary, Manhunter, and Batman.
One is a black cat themed boy who appears to be unconsciously posing for a photoshoot and the other is a ladybug themed girl standing respectfully with both hands clasped behind her.
"Team meet Ladybug and Cat Noir," said Batman while the Parisian heroes shyly(Ladybug) and eagerly(Cat Noir) waved them in greeting, "They are young heroes from France who made debuted last month. The League has been monitoring them from the beginning as potential members of the team. And after their help to several league members from the plant invasion, we have made a decision to invite them as part-time members of the team."
Said team have different impressions: Kid Flash for the thought of getting Ladybug's number; Robin thinking of Catwoman from Gotham; Miss Martian befriending another girl; Artemis thinking of the significance of their outfits for good luck and bad luck.
Short research that French schools start in September and the origin episodes happened in the start of the school year. And Revelation happened in October. I bet Adrien was internally geeking out to see the team considering he's an otaku.
That's all, I just want to put a Young Justice crossover fic for the sake of it. I mean Robin teaching Adrien the art of butchering the English(or French) language. Kid Flash flirting with Ladybug and Adrien being protective to her.