We used to hang out here all the time. We would bring our bikes or roller skates, play tennis, or just watch the kids play on the massive playground they have.
If you want to float the Boise river along the green belt this is the park you need to be at in order to catch the bus. The bus never chargesd us for the kids and we were charged a $1 or $2 per adult.
You can park at Julie Davis park, feed the ducks and then bike over to Ann Morrison Park along the Greenbelt.
There are always lots of people there playing horseshoes or cricket. I saw a lot of soccer teams out there playing. If you are visiting the area it is a great park to take your kids to.