Can I set up a second account for my kid without purchasing the controller and chromecast just the monthly fee?
You can't set up another account on the "free" tier yet, the only way to get access is through the Founder/Premiere kit.
Family Sharing is coming though, but they haven't announced when or exactly how it will work. I imagine that your Google "family group" will be able to share access to one Stadia account at some point this way.
Next year sometime in likely early 2020 when Stadia Base is launched you'll be able to set up other accounts without purchasing anything, however games between accounts wouldn't be shared when doing it that way so I don't think that's what you want either.
Bottom line is you'll have to share the same account in the house for now until we know how Family Sharing will work.
You can't set up another account on the "free" tier yet, the only way to get access is through the Founder/Premiere kit.
Family Sharing is coming though, but they haven't announced when or exactly how it will work. I imagine that your Google "family group" will be able to share access to one Stadia account at some point this way.
Next year sometime in likely early 2020 when Stadia Base is launched you'll be able to set up other accounts without purchasing anything, however games between accounts wouldn't be shared when doing it that way so I don't think that's what you want either.
Bottom line is you'll have to share the same account in the house for now until we know how Family Sharing will work.