Don't know if this is what you are looking for, but for travel: I think MADE starts as early as second grade. They do great with training young kids. Don't know of any that start earlier, but you can check KOA.
I know that HoopEd used to do beginner ballers classes that were for tiny kids.
Also, I think OneOnOne Basketball does (or used to do) some really low key (i.e. not competitive) classes. I was not a fan.