I do think it's the actors speaking on this trailer.
I know of some of the young uns (one in particular who I've seen out & about long before any soul films came along) who are in the film, and none of them are shown in this trailer. I'm pretty certain that they don't have talking parts, and are in the film for their dancing, I could be wrong, and I apologise to any bona fide soul kid that is speaking on this trailer.
Nevertheless, it's still a good trailer, as I can obviously relate to some of the feelings these actors are portraying & it does make me smile