Aishiteruze Baby is another one in this unnamed genre, with a shoujo audience. Romance Papa is manhwa I haven't read, but it's been on my list forever.

a seinen actively comedy example of single young man thrust into childcare
This is very hard to weed out because these are exact genre overlaps with lolicon, which is a genre of AGH AGH AGH when you hit it by accident. The faint vibe of it skeeved me right off the otherwise charming Blood Alone.