Although they'll love the castle and the whole fairytale look of the place, Ljubljana isn't really a top holiday destination for kids. It tends to be better for couples, although there is one great family distraction; a huge new Water Park. It's divided into four sections including Sauna Land with steam baths in an underground cave, and there's also a thermal spa section with massage beds. Another section is strictly for children.
If you're all good at in-line skating and are there in the summer or autumn, join the fun through the city's streets.
Slovenia is very compact, so if you want to see more of the country than just the capital, it's very straightforward. Beautiful Lake Bled is about an hour away and you can hire a boat in order to reach the island castle in the middle.
Alternatively, about 50km away, hop on the electric train and travel through the illuminated caverns of Postojna Caves, the world's second largest cave system.
If you're all a bit adventurous why not head to the Savia River near the town of Medvode. Its rapids are only a few miles away from the city and provide a perfect holiday thrill ride.