There are a number of parks in San Mateo that range in size and amenities. What park is best for you depends upon what you are looking for. If you'd like a small, neighborhood, more quiet park I would recommend the two hidden parks on 31st Ave in San Mateo, above the mall and below Alameda de las Pulgas. You wouldn't know they are there, which is why they are called the "hidden parks". The one closer to the mall on 31st, entrance on 31st and in the Lanes, is a neighborhood, family park where one could picnic quietly. There are a few playground items around such as a jungle gym, slide, and rocking horse. An older tennis court is also present. Up the street, on the same side but closer to Alameda de las Pulgas is the larger hidden park with more green grass and open play area.
If you are looking for a larger park, Beresford Park at the Rec Center is a nice park. It is located at 28th and Alameda de las Pulgas. Here you will find tennis courts, a skate park, a sectioned off smaller children's play area, a large playground area, picnic benches, and a baseball field. A garden is also attached where you could wander through.
If you are looking for a very large park close to downtown, then Central Park is your place. It has a huge play structure and a small train that runs on a track mostly during the weekends. They also sell snow cones there. Riding paths are present throughout the park, and there is also an attached, separate baseball field as well as a number of tennis courts.
Abbie Higashi - 8z Real Estate Broker, 650-799-6204