Did not explicitly address it, though the idea I had in mind is that Chen was attacked by someone else after she ran away. Shou was not seen again after she went to look for Chen.
JusticeItEasy largely had the synopsis I had in mind, though Chen ran away out of fear that her children would have been gotten rid of, and the timeframe between running away and being found was relatively short.
For the most part I let other people interpret ambiguities as they see fit, though I think it would be odd to hunt them down and stab them as punishment - either he'd take them back home, or be content with whatever fate the streets had for them.
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And much MORE!
If you read Kodoku's coment you already know the majority of the story, basically what Anon did was sent the surviving Shou and Chen to the same guy that trained their parents and managed their Pet Badge, all this after somehow finding what remained of his old pets after they ran away from home to not bring him problems with the babies expenses.