I have no experience with children of my own, but i do with my 7 year old brother. You say that the only movies that little children don't go hystericaly crying are those family movies which always end well and as some guy before mentioned, nothing realy dramatical happens, like BAD guys actually dying. I believe this kind of teaching children that everything is ok an well will only have a negative effect on them. If all their childhood they watch movies like that, they will not understand death and think that whatever happens, people will not die or be injured. That could, in one case lead to them growing up and hurting people thinking they'll be ok anyway, or just soften them up to the point when anything sad or tragic they see will cause them to suffer mentaly. I think so, because i have such experiences with my little brother. His mother took him to all of these family films you say are good for children. Before he never saw a film where something bad happens or someone get's injured. When we went to watc wall-e some time ago, in the scene in the beginnig when Eve lands and starts shooting everything around, my brother started crying and complainig to the point where we had to take him out because the people were getting annoyed. After that film, we went to see some more films were not everything was all good and well all the time. The same story repeated itself every time we went to see such a movie and it just got worse and worse. Now we just rather don't take him to pixar animations because we know he'll just end up crying. And that's NOT Pixar's fault. Its the fault of him being raised like you raise your children MadCow, watching goody movies and making the child soft and vunerable to any kind of tragedy. To finish off my post, i would like to point out that Pixar movies are (in my opinion) great and have a better story than other movies of the same genre. The story contains sad parts as well as happy parts and that is what, again IMO, makes the movie interesting to watch and as it ends, leaves a mark and maybe leaves you thinking about it, unlike with other films, say Madagascar, which is a film made purely for entertainment and i think entertainment alone doesn't make a good film.
All that being said, i do hope you will consider raising your kids differently, or we can all aswell become a bunch of brainwashed idiots, thinking that all is well and ok.
-TheCarny