If you liked the Bunny Drop manga, the Anime-Planet community thinks you'd like:
Aoki Daisuke is a fresh, new elementary school teacher, eager to help shape and guide his young students. But he got more than he bargained for with Kokonoe Rin! This saucy third grader has knowledge beyond her years, and a deep-seated mistrust and loathing of adults. She will go to any lengths to protect her friends Kuro and Mimi, including harassment, extortion, threats, and sexual blackmail. And yet, with her friends, she is kind, caring, and self-sacrificing. Can Daisuke gain Rin's trust and save her from her dark side without falling victim to it himself?
While at first they might look completely different, one being josei and slice of life, and the other being an ecchi, lolicon, comedy, they do have some core similarities. Both involve bastard children being raised by single men who are not their biological father. Many times in both drama occrus over who should take care of those children. Both children, also both named Rin ;P, are very mature for their ages. So if you like Usagi Drop and can tolerate panty shots, raunchy jokes and children in sexual situtations give Kodomo no Jikan a try. If you're a fan of Kodomo no Jikan and don't mind fan servicelessness (I made a new word) try Usagi Drop
In both of these series, a young man suddenly finds himself having to raise a daughter. The guy is completely unprepared and experiences many challenges trying to take care of a child when he can barely take care of himself.
Sachiko Azuma felt that her first child, Hikaru, was born to her with the morning light; however, the joy she expected from being a mother was short-lived. Her child exhibited unusual behavior, not wanting to be held, seeming to not hear people when they spoke to him. Being confused as to what was wrong, she sought help from doctors who misdiagnosed the problem. Eventually learning that her son had autism, Sachiko became motivated to learn more about the disorder with the goal that her son could become a working, independent adult. Now, Sachiko continues to face the struggles of raising a child with special needs, while attempting to help seemingly-uninterested people understand more about autism.
With the Light and Usagi Drop are two series about people who are presented with children under unexpected circumstances. The main character in With the Light gives birth to a son who has autism, something she has very little knowledge of, while the main character from Usagi Drop is a bachelor that is presented with an orphaned child, when he has little esteem for children in general. Both are forced to try to cope with the unforeseen developments in their lives, and the stories are told from these new parents' perspectives. With the Light is far more dramatic than Usagi Drop, but both series blend comedy and serious situations.