This is not entirely true. Even the elite who were included in the sanction lists (Russian) are regularly noticed in the EU countries. They can come to rest through diplomatic channels or through bribes. Also children of people under sanctions live mainly in EU or the USA. While they are investing in those countries, they are not asked questions about the origin of the money
I mean seize illegally earned money and/or forbid them and their families spending those money in the EU and other friendly jurisdictions. EU as a whole should have enough weight to make it happen if enough political will is present.