you know what is the saddest thing? they don't seem that bad outside of eating their child, since they greet the mister quite nicely, yet, eating their child in worth can undermine all their good aspects easily...
That's expecting to much from them, believe me, they are capable of eating their little ones it isn't a "weird" bad aspect of them, besides, ketchup can't pass for bean paste, and, yukkuris are made of bean paste and bleed bean paste, ketchup will never ve a good "fake blood" for yukkuris.
Well, they didn't pull the prank off well; Mr didn't even realize that they were trying to pretend that they ate the babies until they said that they were "delicious." It's harder for us to tell that it's ketchup because the picture is black and white.
believe me, if the author wanted us to think that, he would had hinted it, don't stretch farfetched and baseless Ifs for the sake of "not making them bad", it's like if there were hints in the floor of splattered bean paste and some hints of murder and saying "oh well maybe they just are playing a prank on the mister by spreading bean paste and faking a murder"
That's not how it works in 1 shot pics like this, they tend to be quite explicit, or explicit enough.
So no, no ketchup, no prank, nothing, they ate their little ones for some reason and whatever the anon approves or not, is up to the creator, not us.
Yeah don't deserve, Gold Badges aren't meant to do this kind of things, and there is no hint of the anon training them for that specially because of his surprised "Heh?" at the end, that should hint you the idea that he's facing something unnexpected.
I have a feeling the artist just made the situation to make the audience laugh, without thinking of whether the yukkuri couple seriously ate up their children, but then again, the insertion of the gold badge fuels speculation. Oh and the sensitivity of the topic.
1) They give you a emotional reaction, laugh, awww, get sad, etc. 2) Then it give you stuff to think about out of their illogical nature, which leads to people trying to make the best at understanding everything of them.
Long made short they give you a reaction and a piece of mental work to deal with.