The Exploratorium is free on Mother's Day, even for non-mothers. If the crowds get to you, go outside on the Bay View Walkways and sketch some of those bay views.
9:30 Let's meet up before it opens on the wooden people-watching bench structure to the right of the Exploratorium building (see photo below). If there's an impossibly long line to get in we can make an alternate plan.
12:30 We'll meet to share sketches and chat behind the Exploratorium at the end of the pier, at the tables and benches outside the Seaglass Restaurant. (see photo below) If the lines for food/coffee are too long inside, we can walk to some other spot.
Parking can be difficult in this area, but if you have to bring your car you might get lucky. The 4-hour meters are enforced on Sundays so make sure you put money in them.
Otherwise, catch the F streetcar from anywhere along Market Street. (You can sketch the inside of the historic streetcar on the way.)
If the F is too slow to come, or too full of people when it does arrive, the walk from Embarcadero BART Station is fairly painless (10-15 minutes along the waterfront).
There's a bike lane all the way along the Embarcadero.
For comfortable sketching outside, bring a hat, sunscreen, water and, as always in this city, a windproof jacket.
Here are some photos of the wooden bench structure where we'll meet up at the start:
Here are some photos of the tables at the back of the Seaglass restaurant where we'll meet up after sketching.