A parent in Pleasanton, parent of a preschooler and a toddler
It's not the most obvious choice since it's just a fountain in downtown Livermore, but my kids and others love playing in it when it's hot out, and then walking across to the "big ball" fountain. My little ones like to get changed into swimsuits and then we bring some buckets for them to fill and dump out the water. It's a good alternative to a splash pad at a park but never gets all that crowded, and since it's in downtown Livermore it's a good spot to hit up after taking the family to a restaurant. There are a few coffee shops close by so I'll sometimes pick up a coffee and sit on one of the surrounding benches while the kids run around the fountain.