Barcelona's headline sights involve timed slots and queues. The parts children actually enjoy mostly need neither, which makes a family weekend easier than it first appears.
What works
Park Güell — the mosaic terrace, the tiled lizard, the columned hall underneath. The monumental zone is ticketed and timed; the wider park is free and has space to run.
The cable cars. Two of them — the Montjuïc telefèric up the hill, and the harbour cable car from Barceloneta to Montjuïc, which crosses high above the port. Both are the trip for a lot of children.
The beach. Barceloneta is the closest and busiest; Bogatell and Mar Bella in Poblenou are quieter and cleaner, a few metro stops further.
The Sagrada Família interior, which works better with children than expected — the coloured light is immediately striking rather than needing explanation. Book the first slot.
The aquarium at Port Vell, with a shark tunnel.
The Magic Fountain at Montjuïc — a free light and music show on scheduled evenings, seasonal, so check current times.
CosmoCaixa, the science museum, with a flooded Amazon section.
What is harder
Casa Batlló and La Pedrera — interesting, expensive per head, and largely about looking rather than doing.
The Picasso Museum, unless the children are older.
The Gothic Quarter at busy hours — narrow, cobbled, crowded, and hard with a pushchair.
The Ramblas, which is a crowded tourist strip and a pickpocketing hotspot.
Where to stay
The Eixample — flat wide streets, metro access, and apartments with space.
Barceloneta or Poblenou — near the beach, with more room and a quieter night.
Avoid the Gothic Quarter and around the Ramblas for sleep.
Apartments with a kitchen and washing machine are widely available and usually better value than hotel family rooms.
The eating problem
Spanish dinner starts around 9pm, which is late for young children.
The workable pattern: a proper lunch as the main meal, where the menú del día gives three courses for €12–16, an afternoon snack, and tapas around 7:30pm, which many bars serve.
Spanish restaurants welcome children genuinely rather than tolerantly, and a half portion is a normal request.
The two-day shape
Day one: Sagrada Família first slot, then the Eixample and lunch. Afternoon at Park Güell or the beach.
Day two: harbour cable car up to Montjuïc, the gardens and the castle, funicular down. Beach or aquarium in the afternoon, and the Magic Fountain if it is running.
Practical
The airport is 35 minutes by metro or Aerobús.
Book the Sagrada Família and Park Güell before flying; everything else is walk-in.
August is hot and the city is at capacity. May, June, September and October are considerably easier with children.
Sun protection — the beach and Park Güell both have limited shade.