Take the kids out skateboarding at the Berkeley Skate Park. The park is quite large. There's enough space for the kids to find something they like here. If they just want to skate around on a flat area, no problem.
There are two soccer fields located right next to this skate park. If it's a Sunday or Saturday morning, parking can be a bit hard to find.
The park does have toilets. Those are located at the opposite end of the entrance.