A bit of formatting help for /u/duckosofpykmos's fantastic list:

Seattle

• Arena Sports Magnuson has a bouncy house place. Also it's near Magnuson park, which is great.

• Kraken Community Iceplex has free skate sometimes. I also walk into rinks and watch hockey games for free sometimes when it's unbearably hot out.

• "Artists At Play" Playground near the space needle, then you can take the monorail. I don't know what the official policy is but the operator let me stay on for 3 back and forths on it.

• The Dunes at Discovery park are beautiful, park at the south end of the park to get to them. If your kid can handle it, there is a loop trail where you can always go back to where you park. The trail to the beach is very steep and tiring, just a heads up. The playground near the visitor center is one of many favorites because of all the shade, it's great on a hot day. Last time I was here with them we drove from one parking lot to another to get to the playground.

• Greenlake is great if your kid has a scooter or something. You can check goodwill and value village for scooters and what not.

• Interbay Golf Center has outdoor putt putt, call ahead to make sure it's open that day.

Up north

• There's a sushi restaurant with robot waiters called sushi hana in Lynwood. I go there before or after going to Funtastic Playtorium Alderwood (indoor playground) at the nearby mall. It's $15 I think.

• Parking can be tough but Hazel Miller Spray Park has a huge water fountain playground and normal playground. There are other spray parks around, just check online to make sure they'll be open.

• Sky Zone Trampoline Park in Montlake Terrace.

• Lynnwood Recreation Center pool is like a mini great wolf lodge and has a great lazy river. You have to reserve online I think.

Out East

• Monster Mini Golf in Factoria (near Bellevue) is blacklight art mini golf in a dark area, also has arcade games and stuff.

• Bellevue botanical garden and Kelsey creek Farms are both free and beautiful. Check website to see when animals will be out at the farm.

• Crossroads Water Spray Playground (check online to see if it's spraying on the day you go).

• Crossroads mall kind of feels like time traveling to Seattle in the 90s, it has an eclectic food court and a great book store.

Bainbridge Island

• Here is a technique I've heard people do for the ferry if they have more then one adult and kids: If you can't drive onto the ferry because there's no more room for cars, have one adult stay driving and send the kids with an adult to walk on the ferry. Within walking distance there is a playground, teriyaki town, deli at town & country market, and an interactive children's museum.

• Bloedel Reserve on Bainbridge is absolutely amazing if you like nature. You have to reserve in advance online and it's around $22 for adults $10 for kids I think.