Which European cities are good for family trips?

Which European cities do you think are kid-friendly? We're daydreaming about pinching our pennies and possibly taking Toby to Europe this summer (he'll be two!), and I'd love to find a city that would be great with a little rascal in tow.

Which cities in Europe would you recommend for a family trip? Yolanda wrote a brilliant guide to Paris with kids, and Louisa Kamps wrote a beautiful essay on a family trip to Amsterdam. Thank you SO much for any insights! xoxo

(Photo of Berlin by Travel & Leisure)