This happened between Revalation/plant invasion and Humanity. And the lucky duo still don't have the identity reveal.
They were called by Batman to gather in the mission area. After the 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 bird and the bat.
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 respectively 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 heroes from Paris who started their career since September. The League has been monitoring them from the start as possible members of the team. They protected their city from the recent worldwide plant invasion, so the league decided to invite them as honorary 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.
(Story is also posted in the crossover section)