I think that I'm in general agreement with the OP, but I think two tags should jointly be added. One for “child-rearing” and one for “family-building”
For example, the protagonist in Isekai Yururi Kikou: Kosodateshinagara Boukensha Shimasu is fostering two godlings; were he female, his rôle would be more akin to that of a nanny that that of a mother, and the godlings don't refer to him as a father. A child-rearing tag could also be applied to series such as Gakuen Babysitters and T-sensei.
So, really, four tags have now been proposed in this thread: [ul]a tag “about the protagonistraising a family”,
a Child-Rearing tag,
a Family-Building tag,
a Family Life tag. [/ul]