I have so many things that are wrong with this novel, but I still read it... So let's start!
The bad parts:
1. Better name would have been "Immortal Caretaker Dad", I just don't see why anyone thought nanny was a good choice.
2. "Showing not telling" is a popular sentence in writing that this manga still doesn't seem to know.
3. There are actually quite a few examples of bad writing in this novel from pacing issues to grammar errors, to stilted dialogue.
4. One dimensional characters that only serve one purpose, characters that exist solely to further the plot and are thrown away soon after, etc. Most commonly this is on the villains of this story, but not limited to them.
Now for the actually good parts~
1. The characters are endearing.
2. The story itself isn't that bad... at times.
3. The drawings are nice.
4. The characters that aren't one-dimensional are actually pretty well developed.
Final score: 5/10 it's not a bad manga to waste your time in, but there are probably better things to read if you are not bothered to search.