I got the feeling that Wakaba is not his child but the child of a relative (sister, brother, our cousin) that die and leave Wakaba into his care and that's why Wakaba does not call him dad.
But most kids call their parents by their first names when they're little...?
Oh my gawsh, I Agree!
I bet the child is the son of his sister, relative, or friend? and both of his real parents pass away during an accident or something. That's why he doesn't call Kazushi daddy. That's also why the daycare seems to know so much about Kazushi and the kid's situation already. Most importantly, that's why the kid was trying to ride the the cable car to find his real mommy and daddy. Maybe he was hoping that the cable car would reach to the sky where his parentsi s at. lol. Just a theory.
This was so cute!!!!(๑•ㅂ•)و✧
Wish there was more I love it but it was to short ╥﹏╥