Are taxes a kind of theft?

No. Theft is illegally taking something which belongs to someone else. As taxes are levied by governments, they are inherently legal provided that they don't violate more fundamental laws. (For example, in many countries a law requiring people of particular religions or races to pay tax at a higher level than others would be illegal). Further, taxpayers receive services in return for their taxes. The idea that 'taxation is theft' is an extreme libertarian slogan and makes as little sense as the slogan 'property is theft'.