I always try to have my kids learn a standing back handspring before I do the roundoff backhandspring series. But as mentioned above the only time they do a single standing backhandspring is in level 6.
While I've tried to teach kids to do a bounce back handspring on tramp ( where they bounce forward and get themselves angled backward before bouncing into the back handspring ) and then connect this with a decent turned over RO, they don't just seem to be as willing to connect it until they can do a standing.
I still believe I can teach, particularly lil ones, to do a backhandspring out of a good RO, if they understand the feeling of a BHS and how to hit the hand support and snap down/thru.
Still in practice, any one of my gymnasts will do a standing before connecting it. Possibly, BHS-BHS, or at least a snap down - BHS.