No EU-regulation for that I think, it depends on the country. British Standard 1363 has had mandatory safety shutters since it was introduced in 1947 (not sure if you could still use the older British Standard 546). Here in Sweden there is a building regulation from 1988 stating outlets should be placed or designed to make it hard for children to insert things into them. I was surprised to learn that wasn't common in the US, at least until recently.