I saw this anime movie when I was young,now I’m 21. The movie is about of two kids group which they make war between them with kids toy gun and mud etc. and i think war for a tree house or a tree fortress…….ok and a scene I’m also remembered that a boy and a girl taking and also a short lip kiss to.
Though it’s not animated, that sounds like the plot of “La forteresse suspendue” from 2001. The English title is The Hidden Fortress.