This site has lots of free downloadable resources and planning documents covering WW1 for teachers.
Teaching about the First World War in primary schools can be problematic to say the least. Not only is it a sombre topic in general, but it is also emotive, connected as it is with the sacrifice of those involved, often in horrific and tragic circumstances.
But this doesn't mean that you can't teach about WW1 in your primary school. This site offers lots of free advice and resources to help overcome the difficulties.