First pedal the bike and watch everything in the rear and see whats turning or not, if all the chains are moving I would check the rear sprocket that is on the axle, if only the main chain is turning and the secondary chain ( one going to the axle ) is not it is a hub problem. I don't like the way your chains look, very, and I do mean very dirty and looks like the lube turned to tar, this could also be a problem for the hubs and if it has one the freewheel, if the lube in the hub is like this I would have to take apart and clean that crap out of there. If the rest of the bike is in good shape fix it, the newer cheap trikes aren't built as good as the old ones, they might just look better because they are new lol.

Glenn