Slovenian tourist tax law is detailed in the zakon o spodbujanju razvoja turizma (ZSRT), which is the name of the parliament Act on the Promotion of Tourism Development. Link for English translation.
Generally this is a tax of between €0.60 and €1.25 per person per night, but it does vary by both location and hotel grade. In Llubljana there is a daily tourist tax of between €0.62 and €1.25, whilst in Vaneča, Fokovci, Vino and Moravske Toplice the tax is currently €1.01 per person per night for adults.
The reductions/exemptions applicable to children also vary from place to place. For example using the above destinations: in Llubljana at least one hotel states children aged between 3-12 get a 40% discount and those aged under 3 are exempt; whereas in Vaneča, Fokovci, Vino and Moravske Toplice it is a uniform 50% discount for children aged between 7 and 18, with those under the age of 7 exempt.