Start with Chapultepec, and give it a full day
Chapultepec is the obvious first move and it earns the space. The park is enormous, so pick two anchors rather than trying to cover it: the Castillo de Chapultepec on the hill and the Museo Nacional de Antropología at the eastern edge along Paseo de la Reforma. The castle is a steady climb on foot or a short shuttle ride, and children generally enjoy the ramparts and the views over the city more than the furnished rooms. The anthropology museum is vast; two or three halls, the Mexica room above all, is a sensible limit before attention goes.
Getting there is easy on Line 1 of the Metro to Chapultepec station, which puts you at the park gate, or by taxi and ride-hailing apps to the Reforma entrances. Weekdays are quieter than Saturdays, when the park fills with local families and the paddle boats on Lago de Chapultepec draw long queues. Bring water and snacks, since kiosk food inside the park is basic. For a base, hotels along Reforma and in Colonia Juárez put you within a fifteen-minute walk of the main gates, which matters when small legs tire in the afternoon.
Coyoacán is the gentlest half-day with children
Coyoacán suits families better than its reputation suggests. The Jardín Centenario and the adjoining Plaza Hidalgo form a car-free square with benches, street performers and ice cream sellers, and the cobbled streets around it are flat enough for a stroller. The Museo Frida Kahlo, the Casa Azul on Calle Londres, needs timed tickets bought online in advance and honestly tests younger children; the Museo Anahuacalli further south, designed by Diego Rivera, holds more interest for kids who like dark volcanic stone and echoing halls.
Reach Coyoacán by Metro Line 3 to Coyoacán or Viveros station, then a ten- to fifteen-minute walk, or by taxi from the centro in roughly twenty-five minutes depending on traffic. The Mercado de Coyoacán, a block from the main square, is the practical meal stop: tostadas, quesadillas and fruit waters at stalls with tables, casual and quick. Sunday is the busiest day, when the square hosts a market and the crowds thicken by midday. I would book a hotel in Coyoacán itself for a slower stay, or in Roma Norte if you want to combine it with the centre.
The centro rewards a short, focused morning
The historic centre is dense and hot, so keep the visit short. The Zócalo, the Catedral Metropolitana and the Templo Mayor site sit within a few blocks of each other, and the excavated Aztec ruins with their museum are compact enough for children to absorb in an hour. The Palacio Nacional murals by Diego Rivera are free to view with photo identification and a short wait, and they give a vivid picture of Mexican history that lands well with older children. Skip the long museum corridors and stay outdoors where you can.
Arrive by nine in the morning to beat the heat and the tour groups; the Metro Zócalo station on Line 2 drops you at the square. Walk a few blocks west to the Palacio de Bellas Artes for the exterior and the adjoining Alameda Central, a shaded park with benches and fountains that makes a natural rest stop. Meals near the centro are easy: the Sanborns branches and the cafes along Calle Madero serve familiar food quickly. Hotels around the centro and Colonia Guerrero are the budget option; expect noisy nights and check the room before booking.
Xochimilco, and how to fit it in
The canals at Xochimilco are the day children remember. Colourful trajinera boats leave from the embarcadero at Nuevo Nativitas, and a shared boat ride runs about an hour through the chinampas, the old island gardens. Prices are set per boat rather than per person, so groups should negotiate the rate at the dock before boarding; the smaller embarcaderos tend to be calmer. Weekends bring food stalls and mariachi on the water, which is festive but loud; a weekday morning is more peaceful with young children.
Reaching Xochimilco takes effort. The Tren Ligero from Tasqueña station, at the end of Metro Line 2, runs south to Xochimilco and then a short taxi covers the last stretch; allow an hour from the centro each way. Pair it with the Museo Dolores Olmedo if it is open on your dates, and skip it otherwise. For families who want one base, I would book in Roma Norte or Condesa, where parks, cafes and easy transport to both Chapultepec and the centro meet, and take taxis to Xochimilco rather than relying on the metro with tired children.