Lisbon is genuinely welcoming to children and it is built on seven steep hills paved with polished limestone. That tension shapes the whole trip.
The hills, practically
Alfama, Graça and Bairro Alto are steep, stepped and paved with calçada — small polished blocks that are slippery when wet and hostile to wheels.
A pushchair there is hard work. A carrier is easier for younger children.
Base in Baixa, the flat grid between the hills, or in Parque das Nações, which is modern, level and spacious.
The funiculars and Elevador de Santa Justa are public transport covered by a transport card, and children generally enjoy them.
What works
The Oceanário at Parque das Nações — one of Europe's largest aquariums, built around a single vast central tank circled on two levels. Reliably the highlight.
Around it: a cable car along the waterfront, the Pavilhão do Conhecimento science museum, and open flat space to run.
Belém — flat, riverside, with the Coach Museum's gilded carriages (better with children than it sounds), the monastery, the tower, and the original pastéis de Belém.
São Jorge castle — walls to walk, peacocks, a view. Take a tuk-tuk or the 737 bus up and walk down.
The beaches — Carcavelos and Cascais on the train line from Cais do Sodré, half an hour.
The ferry to Cacilhas, which is a boat trip for the price of a fare.
The tram question
Not the 28. Packed to the point of discomfort and the city's main pickpocketing location.
Tram 15 to Belém is modern with room for a pushchair. Tram 12 covers similar ground to the 28 with far fewer people.
Sintra with children
Pena Palace works — brightly coloured, on a peak, fairy-tale in appearance.
Quinta da Regaleira works better for older children, with its initiation wells, tunnels and grottoes.
The difficulty is logistics: steep walks, queues, crowded buses.
Go early, buy timed tickets in advance, pick two sites rather than four.
Eating
Portugal is straightforwardly child-friendly. Restaurants welcome children and the food is uncontroversial — grilled fish, chicken, rice, soup.
Caldo verde, the potato and kale soup, is a reliable option. Frango piri-piri can be ordered mild.
Meal times are less extreme than in Spain — dinner from 7:30 or 8pm.
The couvert, brought unasked, is charged if eaten. Refusing it is normal.
Practical
Viva Viagem card for metro, trams, funiculars and buses. Children under a certain age travel free — check the current threshold.
Apartments with a kitchen and washing machine are widely available and usually better value than hotel family rooms.
Spring and autumn are considerably easier than summer, when the hills are hot and the miradouros have no shade.
Shoes with grip, for everyone. The paving is genuinely slippery.