Leave Petaluma around 8:00 AM and take US-101 south, then follow the most straightforward route into downtown San Francisco; if traffic is light you can make it in about 1 hour 15 minutes, but on a summer Saturday it’s smart to budget closer to 1 hour 30–1 hour 45. Because you’ve got a 2-month-old in tow, I’d aim to park once near your first stop and minimize car shuffling for the day — a garage around Yerba Buena or near Howard Street is usually the easiest move for SFMOMA. Expect city traffic, some lane changes around the Bay Bridge approach, and pay attention to garage clearance if you’ve got a larger vehicle or stroller gear.
Spend late morning at San Francisco Museum of Modern Art (SFMOMA) in SoMa, which is one of the easiest big museums in the city for a multigenerational group. It’s fully indoors, stroller-friendly, and calm enough that grandparents can enjoy the galleries at their own pace while parents take turns with the baby. General admission is typically around $30–$35 for adults, with discounts for seniors and free/low-cost options for young children depending on current policy; plan on about 1.5–2 hours here, but don’t feel pressured to see everything. The best part is the open layout — you can duck in and out of exhibits, find seating when the baby needs a break, and keep the day from feeling rushed.
For lunch, head to The Rotunda at Neiman Marcus in Union Square, which is a classic San Francisco lunch stop with a beautiful atrium and a slower pace than most downtown restaurants. It’s a good place to sit down as a family without the noise and turnover of a café, and the setting itself feels like part of the outing. Expect about $25–$45 per person depending on what you order, and allow roughly an hour so nobody feels rushed; if you’re coming straight from SFMOMA, it’s an easy short walk or a very quick drive, though with a stroller I’d usually just walk if everyone’s comfortable. It’s indoors, air-conditioned, and a nice reset before the more hands-on part of the afternoon.
After lunch, make your way to the Exploratorium on the Embarcadero, which is one of the best all-ages indoor activities in the city — especially for a family group that spans baby to grandparents. It’s interactive without being overwhelming, and you can keep it flexible: wander a few galleries, pause when the baby needs feeding or a diaper change, then keep moving. Admission is usually in the mid-$30s for adults, with children under 3 often free, and 2 hours is a very workable visit length. If you parked earlier near Yerba Buena, it’s a short rideshare or Muni/taxi hop across downtown; if you’re driving, the museum area has garages nearby, but Saturday afternoon can fill up, so use whichever option feels least stressful.
Finish with a relaxed stop at The Ferry Building Marketplace, which is perfect for coffee, dessert, or an early dinner without committing to a full sit-down meal. It’s mostly indoors, easy to navigate with a stroller, and has enough variety that everyone can choose something different — a pastry, tea, oysters, cheese, sandwiches, gelato, or just a coffee while you decompress by the waterfront. Budget roughly $15–$30 per person depending on what you pick up, and give yourselves about an hour so you can browse without rushing. If you’re heading back to Petaluma afterward, aim to leave the city before the evening bridge backup builds too much — usually around 5:00–6:00 PM is the sweet spot — and take US-101 north home; if traffic is still moving well, you’ll usually be back in about an hour to 1 hour 30 minutes.
Leave San Francisco after a slow start and head straight to Golden Gate Park for California Academy of Sciences; from most central neighborhoods it’s usually a 15–25 minute drive, or a straightforward bus/ride-share if you’d rather avoid parking. If you’re arriving from the city side, use the Music Concourse Garage or nearby metered parking and plan to be inside by opening time so you’re not juggling the baby and a crowd. General admission is usually around $40–50 for adults, with discounts sometimes available for locals, and it’s absolutely worth booking timed tickets in advance on a summer weekend. Give yourselves 2.5–3 hours here: the aquarium is calm and stroller-friendly, the Rainforest Dome is warm but manageable if you keep the visit short, and the planetarium is the big sit-down moment for adults while baby gets a break.
Walk or roll over to the de Young Museum, which is just across the park and makes a nice change of pace without adding much transit stress. It’s quieter than the Academy, and the wide galleries, benches, and elevators make it easy to move at baby speed; admission is typically around $20–30, and there’s usually a good coat-check area if you’re carrying extra gear. Stay 1.5–2 hours, focusing on whatever rooms feel least tiring rather than trying to see everything. Then head to Kokio Republic in the Inner Sunset for lunch — it’s a reliable, low-fuss stop for ramen, rice bowls, karaage, and kid-friendly takeout if someone in the group wants to eat lightly. Expect about $18–35 per person depending on drinks and add-ons, and it’s the kind of place where you can get in, eat, and get back out without losing the afternoon.
If everyone still has energy, keep the pace gentle with a short visit to the Japanese Tea Garden back in Golden Gate Park. It’s a mostly shaded, compact stroll rather than a destination you need to “do,” which is perfect after a museum-heavy morning; give it 45–60 minutes max, and skip anything that feels like extra walking with the baby. If the weather turns windy or the group is fading, it’s completely fine to treat this as a brief look-in and then head for the car early. For the drive home, leave San Francisco around 3:30–4:30 PM and take US-101 north back to Petaluma; on a Sunday that usually means about 1 hour 15 minutes to 2 hours depending on city traffic and bridge backups. If you want a no-sun, indoor break near the route home, Marin County Civic Center area or a quick stop at a mall-side cafe in San Rafael can make the return trip easier before you finish the weekend.