VISA
Many visitors to Greece will not need to obtain a visa for visits to Greece of up to 90 days. This includes citizens of all other European Union countries, Canada, Australia, Japan, and the United States. These days, as security arrangements change rapidly, visa requirements can also change. If you're flying directly to Greece, your airline may also be able to tell you if a visa is required, but it is best to verify visa requirements for Greece with the Greek embassy or consulate in your country.
For information about VISA requirements you can consult the Greek Ministry of Foreign Affairs: http://www.ypex.gov.gr/www.mfa.gr/en-US/Services/Visas/Visas+for+Foreigners+travelling+to+Greece/
Make sure that any children travelling with you either have their own passport or ID card or are registered on your passport.
For travelling in Europe:
http://europa.eu/abc/travel/index_en.htm