Whatever the sample labeled 3A has came from – it had mtDNA with mutations unknown in any human, primate or animal known so far. The data is very sketchy though and a LOT of sequencing still needs to be done to recover the complete mtDNA sequence. But a few fragments I was able to sequence from this sample 3A indicate that if these mutations will hold we are dealing with a new human-like creature, very distant from Homo sapiens, Neanderthals and Denisovans.. I am not sure it will even fit into the known evolutionary tree. The question is if they were so different, they could not interbreed with humans. Breeding within their small population, they may have degenerated due to inbreeding. That would explain buried children – they were either low or not viable.