He was very aggressive and often found it hard to control his anger which often led to him lashing out at his parents. Even Jo had to bear the brunt of it as River chased her during Observation, throwing balls at her, hitting her in the privates and repeatedly jabbing at her.
When Corey put River in timeout, a full blown fight between River and Corey began. River kicked Corey in the groin, scratched Corey on the neck, put boogers on stuff and trashed the timeout room.
He was 6 years old at the time and is now 16 in 2017.
River's IMDB page - Not as detailed as Hunter's page. He seems to have done a lot of the same background work as his brother.
River's Facebook fan page - Very similar to Hunter's page