I hate to be the one giving examples but here are my 3 fav manga/manhwa/manhua with this specific topic:
Our Sunny Days
Whose Baby Is It?? (Though stopped midway cause stepbros being lovers was weird asf)
Dysfunctional Family Therapy ((mangga) loved this so much probably read for like 5 times already)
i was gonna suggest 'whose baby is it' and 'dysfunctional family therapy' but then saw your comment T_T
check out 'like a tidal wave'. it's a really good omegaverse story (super green and hilarious too), but there's no kid in it for a while. there is one, however, in the side stories. it's pretty good! i'll prolly drop more recs if i remember them; this is the only one that's on my mind right now ^_^

Guys, I seriously can't move on from Our Sunny Days, because it's literally the best thing everrr. It's literally perfect, can anyone reco me something like that? Where a single father finding a good partner. Yk, a real found family. A single dad, and then a father who stepped up. Cause I CAN'T (for the love of G) somehow can't read manhwa/manga with children but I still have to wait for the mc to get pregnant