Very shallow. Shallower than a shallow thing in fact 
Right: This place is just great. Kids or no kids it's a lovely place to eat. Not expensive at all, about 15/20 minute walk from Las Ramblas and DELICIOUS food. You can't book, but for supper I'd get there just before 8ish or 1 for lunch.
There's a good Hard Rock at the top of Las Ramblas, and mid way down Las Ramblas is Boqueria THE most fabulous food market with amazing tapas places. It's just an awesome sight (for me as a foodie anyway) and it's fun (for me...) to have a variety of tapas at several of the places within.
On a not so sunny day I would recommend going to Port Aventura, either to the waterpark or the theme park itself.
There is a great aquarium in Barca too.
Las Ramblas is FULL of great street entertainers, like Covent Garden but more, and the Olympic site down at the beach is also loaded with great bars and restaurants.
Obviously there is all the wonderful architecture (practically makes me weep...) and walking down Paseo de Gracia there are some of Gaudi's buildings (and top notch shopping...).
The main hub is Plaza de Cataluña, off which runs Ramblas and Gracia, and you can also get tour buses from there as well.
Have a WONDERFUL time, it is one of my 3 favourite cities in the world.