After looking through kiku's list for cutest little girls in anime I decided to start my own list to find the cutest little boy in anime. To start things off I'll add my own list first:
-Suzune Kujyou (Kamichama Karin-chu)
-Minoru Enoki (Baby & Me)
-Mao (Chibi Devi)
-Ruu (UFO Baby)
-The young Usami and Hiroki (Junjou Romantica)
-Negi Springfield (Negima!)
-Chibitalia and Holy Rome (Hetalia)
-Aladdin (Magi: The Labyrinth of Magic)
-Ciel Phantomhive (Black Butler)
-Young Gilbert Nightray, Young Vincent Nightray, and Cheshire (Pandora Hearts)
-Reborn ( Katekyo Hitman Reborn)
-Ranma (Ranma ½)
And finally Ikuto and Tadase (Shugo Chara)
I choose ranma http://anime4fun.com/?s=ranma+1%2F2
Feel free to add on.