Hooped Nation holds classes, camps and maybe leagues too. I’d recommend signing your child up for Fall training classes then sign up for a winter league. It can be challenging for kids to start up on a team as a beginner.
https://hoopeducation.com/schedule/
My son learned to play basketball at a summer camp pre-k! He had great first time league experience through DC Parks & Rec. Many Rec Centers host teams for youngers.