[TOMT] [MOVIE] a Japanese movie about a group of kid (elementary school) who run away from class

so i watch this around 2013-2014, so this movie is release before 2015 forsure, the movie is not that old i think is from early 2000s-2010s, the movie about a group of kid 4-5 i think, they want to run away from class to do something i forgot, what i remember there is a scene that the kid carry his dead dog in his bag