I've been watching the new Disney Plus shows as they come out, and in the latest episode of Falcon and Winter Soldier, a character is shown, but doesn't even have a name, except in the credits, and was a relation to another character that I didn't even know about, but the implications are that they've revealed another Young Avengers team member. The speed with which they're hinting at and seeding subtle hints into various movies/shows for that roster is interesting, because it makes me think that Marve/Disney is feeling the time crunch of having their actors get too old, or too famous/expensive to keep using as the "Avengers".
So who are the Young Avengers? They're a team of teenage superheroes that tend to have some sort of tie to various older superheroes. They were never really an "official" Avengers team, that I know of. As in they didn't ever really have the endorsement of the adult Avengers to run around using their name.
There are some mild spoilers for movies/shows ahead.
So who have we seen from the Young Avengers roster so far?
Cassie Lang, Scott Lang's (Ant-Man) daughter. She gets access to Pym particles, and becomes the size changing hero "Stature", she then loses that, and eventually gets stuff more like the Wasp's and becomes "Stinger". Seen in the Ant-Man movies, and they aged forward rapidly in Avengers Endgame thanks to the time jump between movies.
Billy Kaplan and Tommy Shepherd, Wiccan and Speed - There's a lot of weirdness to them, but to summarize Scarlet Witch and Vision have twins, through magic, one gets the powers of Quicksilver, their uncle, and the other Scarlet Witch's powers. We'll ignore why they have different surnames, suffice to say that they're born in the WandaVision tv series.
Eli Bradley, Patriot - This is the one I didn't know about. Patriot's been in a lot of stuff I've read, but I'd never seen his origin story, and they've started to seed it in Falcon and Winter Soldier. After Captain America "dies" in World War I, the US army experiments on a BUNCH of black soldiers to try and recreate the Super Soldier serum. This was literally designed as depressing comic book take on the numerous times that black americans were used in experiments and trials without informed consent. Of the 300 soldiers experimented on, only one survived, Isaiah Bradley, who went on one suicide mission, but decided to do it in Captain America's uniform, so he stole it. The mission was successful, but he was court marshalled for stealing the uniform, and thrown in jail for 30 years. Eli is his grandson, who after getting a blood transfusion from grandpa, got some super soldier powers and took up the name Patriot.
Now the rest of these are more supposition/established background elements than they are characters that we've ACTUALLY been shown:
Teddy Altman, Hulkling - Teddy is the son of a Kree and a Skrull, two alien races that hate each other and have been waging war against each other for longer than human history. The idea two of them would fall in love and have a baby is kind of analogous to the idea of an angel and a demon having a love child. Kree dad gets killed for the crime, and his skrull mother runs off with him and hides out on Earth to raise him as a human. He has super strength, because his father was a Kree elite, and shape shifting powers because of his skrull mother.
Kid Loki - If you thought Wanda's kids were weird and magical. So at various points in the comics, Loki has been punished by being forced to his childhood self (losing much of his memories of his time as an evil bastard). So Kid Loki is sometimes just the current Loki, SOMETIMES, though, he is Loki's memory of being Kid Loki that manages to manifest separately and run around as a completely autonomous entity, he's even worked at odds with his adult self. This one is MUCH more speculative, but in Endgame, an alternate reality version of Loki from right after the first Avengers movie (so pre-redemption) manages to escape with the help of the Space Infinity Stone. The next Disney Plus show after Falcon and Winter Soldier, is Loki, which features him on the run from/or working with the Time Variance Authority. The TVA are literally Marvel Comics' time cops. I could absolutely see time travelling Loki shenanigans resulting in the introduction of a tween incarnation of everyone's favorite god of lies.
Nathaniel Richards, Iron Lad - If you felt I was reaching for Kid Loki, let me tell ya. Nathaniel Richards was born in the 30th century. He is distantly related to Reed Richards of the Fantastic Four, and allegedly a direct descendant of Doctor Doom. He becomes an adult, assumes the moniker: Kang the Conqueror, and conquers the entire milky way and brings peace, under his iron fisted rule. He further decides that the only real way to keep his dominion safe is to go back in time and conquer the galaxy in the past. He becomes a repeat antagonist to the Avengers and the Fantastic Four.
Here's where things get fun, Kang LOVES time travel, he just can't help himself, on multiple occasions he interferes with himself at different stages of his life, pissing himself off, and those different iterations spin off alternate forms of him. Thus we have Immortus, the Scarlet Centurion, and Rama-Tut. Who were all introduced as different time travelling despots from the future that were trying to conquer the past and fought the heroes of the 20th century. Eventually it was revealed that all shared the same past as a kid named Nathaniel Richards born in the 30th century, before splitting off into their own thing.
When Nathaniel was a teenager, Kang travelled back in time to talk to himself, and young Nathaniel was so upset that he became a villain that he decided to take a bunch of future tech, build himself a super suit, and travelled back to the 20th century and be a hero under the name "Iron Lad".
Now, what's my tenuous connection to what's been revealed about the Marvel Cinematic Universe? Remember that the Loki TV show is primarily about his interactions with the Time Variance Authority? One iteration of Kang the conqueror created and runs the TVA.
So yeah, that's everyone/everything I can remember that's been hinting, or setting up the necessary background for Young Avengers characters.