Always check dates for submisions and entry requirements carefully, and check they have a suitable slot for your type of film
These festivals have stood the test of time
www.firstlightmovies.com Has a list of festivals for young people and others which have a childrens catagory.
www.filmfestivals.com Search engine by country and month.
www.netribution.co.uk/festivals Out of date but has comprehensive listings with search engine.