First, park the car at a Max Parking station, buy day passes for the family, and ride around using the Max and/or bus (kids will love it). Take the max to downtown for Voodoo donuts for Breakfast.
While downtown, check out the Saturday Market under the bridge.
Take the Max and/or bus to OMSI (submarine for sure if you go) or Zoo for entertainment. Max has a train that goes directly to the Zoo, and a max with a bus transfer, and a decent walk to Omsi.
Ride the new sky tram for pictures if near Omsi.
For Dinner, if you want something different, and the kids don't mind, go to Marrakesh for a Morrocan dinner and fun. Otherwise consider Brazil Grill, Old Town Pizza, or Flying Pie Pizza.
Could also check out Oaks Amusement Park or Bullwinkles in Wilsonville.