They can do Robin in the Reeves movies, just don't have him starting out as a 12 year old like in the comics. Make him like 16. Still a kid but old enough to be somewhat realistic.
If the MCU can have a child be recruited by Tony Stark to go against his former friends in a superhero civil war, entrusted with advanced technology, fight an alien who wanted to wipe out half the universe, to fight two disgruntled guys who had beef with Stark, and to fight powerful villains from multiple universes, all before graduating high school, they can have a kid fight against the mafia, a homicidal clown, a dude with a fukked up face that has a personality disorder, a dude obsessed with riddles, and a crazy dude obsessed with Alice in Wonderland.
Also wait until the third movie or end of the second movie. The Batman takes place in Batman’s second year of fighting crime and Robin became his partner in his third year.