We were just as disappointed. One user suggested that the cover+title without any context made it out to be a heavy loli VN, which... Is gross and I really hope is untrue. I'd rather the failure be due to the lack of sex appeal than people thinking this was some kind of pedo game.
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I had this game on my list of favorites from long ago, and I logged in just today not even remembering about it, so I saw the cover image and to be honest, I almost for a second thought it was a lolicon VN for a moment, until I clicked on it to be sure (since it was on my favorite list and all) and read the description to find out it was just a parent-child...
It is sad that I had thought that even for a second, but it is unfortunately a real thing even for someone like me who is extremely anti-lolicon, or maybe because of that, people like me end up overly cautious with cover images showing a child character (whether or not there is sexual context). It probably also didn't help that in my case, all of my other favorited things were BL, so surrounded by those cover images of sexually attractive guys was this one, it did throw me off for a moment.
It is sadly mostly due to a reputation created by the lolicon/moe movement in anime fandoms, and how popular lolicon is nowadays, that causes a lot of prejudice and suspicion when any underaged moe-anime-style characters are shown in cover images. Even wholesome anime about parenting like Aishiteruze Baby which usually features a 5 year old girl and high school boy on the cover, will likely have some people on edge until they read about it or watch it to find there is no lolicon or pedophilia appeal in it.
When I went to Canada which has arrested people for bringing in lolicon, the border patrol in the airport was extremely cautious towards me as well, ended up going through all of my phone and computer pictures for about 2 hours, and it was likely because I had anime pins on my bag that I was flagged (even though the pins were of adult guys from Hakuouki), and I could tell they were looking very suspicious anytime there was any younger looking anime character image even if it wasn't sexual (such as screenshots from random high school anime).
Even though I know the game is majorly about fatherhood, it might just to prevent misunderstanding, be safer to remake the cover image without the child, even though the child is a major character in the game and not sexualized.
I think also because of many visual novels involving romance, there is the common initial assumption that whichever 2 characters are shown on the cover are the lovers.