Dennou Coil, Made in Abyss Recommendations
Both have kids investigating something mysterious.
Both have great animation above some TV Anime.
Both have similar character design.
Both titles feature a bespectacled female protagonist searching for someone/something from their past and smart, curious children, eager to explore the world around them. There are hints of dark secrets lurking in the Abyss and behind Dennou Coil's Augmented Reality.
Among the anime I've seen these 2 probably share the most similarity in an overarching sense. Both have rich and fantastically elaborate worldbuilding that continues to surprise the viewer with mysteries and secrets until the end. Also, the young characters and initial child-like wonder belies some rather dark and bittersweet themes. The kids in both cast are written well and realistically (which I find rare in anime). Both have distinct animation style and quality even though the art looks simplistic. And let me just emphasise again how incredibly original and imaginative they are!
Aside different settings - Dennou Coil more science fiction and Made in Abyss an engaging fantasy adventure - but both share a curious, adventurous and youthful main cast as well as the driving force is a heartily girl.
Both series let their little heroes go through life's bitterness-sweetness, with disappointments and hardships.
The story lines in both shows are well written, offering the opportunity on the one hand just to watch and enjoy or, on the other hand, to watch attentively and think about the questions and thoughts raised.
I would like recommend both anime because (IMO) both are worth your time.
Both the anime depicts the small kid investing unknown domain which contains unknown threats and lesser adult intervention.Both the anime provides us with a sense of adventure and mystery which is well maintained.