If you liked Kotaro, I bet you would love the Yuzuki brothers! Similarly, children from those dramas had 'lost' their family at a young age and the drama revolves around the relationships they had formed. This is what I search for a slice of life family dramat but both offers extra cuteness since the main cast are these children who are really great in acting for such a young age. I would often break a tear but the over-all atmosphere of these two dramas is warmth (and cute).
At first one may think that the common ground with these family dramas are just that their stories are child-centered with Shin and Akiko doing the best for Kotaro and Miyuki respectively. If you like Akiko's personality, you probably would like also Kotaro's and vice versa. Both have comedy elements and gives off that warm feeling you often get with good jdramas.