1st trip... 9 days with a 9 year old... In Washington State.
Head for Winthrop, WA. via Moses Lake (stop at Dry Falls info center)
Grand Coulee Dam has a neat laser show at night.
Bridgeport has cool carvings down it's main street. (and a nice city cg)
Past Pateros and north to the Methow Valley.
There's a Good Sam park between Twisp and Winthrop.
There's a nice WA state park near Winthrop.
Tour the NORTH CASCADES Smoke Jumper base between Twisp and Winthrop.
Have ice cream in Winthrop.
Drive up to the top of Washington Pass on hwy 20... and keep going
but first, maybe Drive over to Chelan and take an airplane tour of the North Cascades.
Do all of that... and you'll just have time to get back home before your 9 days are up.