Complex sentence: He misses, loses control of his bouncing and crashes into the shelves of toys, knocking most of them off, before careering outside and landing on his backside in the cacti on the stall.
Split into simpler sentences: He misses, loses control of his bouncing, and crashes into the shelves of toys. He knocks most of them off before careering outside and landing on his backside in the cacti on the stall.