In the USA we do have ways of tracking the offenders. Do you have this in Poland yet? I can search any area and see where they reside after released.
They also cannot live near schools, work that puts them in contact with children and many cannot have contact with children under 18 years of age.
Unfortunately the tracking idea would need a big change of law in Poland, due to very strong privacy laws. Newspapers can't even print the surnames of people convicted - they can only say, for example Jan K, or ks Piotr Z.
Also the rules about who can work with children are extremely primitive. In UK when the system of checks was introduced there were massive delays and a few sad mistakes. In Poland all that is needed is a Certyficat Niekaralnosci (and not always that!!), which can unfortunately be obtained in small towns by bribery.
It would be a good idea to have a Europe-wide (if not worldwide) system though, due to increased mobility of workers, perhaps based on the American system, perhaps a combination of that and the UK system. Both have their strengths and weaknesses. In the UK, they can say that a paedophile lives in your area, but they very rarely name them. This has led to people being attacked by lowlife, just for being a bit weird, while the real paedophile goes unnoticed. Some say the US system forces them to go underground. There must be a system that's foolproof.