Is one of the main important topics on the history of EU, even it belongs to the past and is not so appealing for pupils. While studying EU from its beginning it's fundamental to know which are the founding Countries and the founding Fathers of the first IDEA of Europe as a union of citizens.
The official website to refer to is always the root of all information
Here the specific LINK to the topic
Also this LINK is interesting https://storify.com/OneEurope/the-founding-fathers-of-the-european-union