unable to change passcode on Watch SE for family member

I used my iPhone 12 Pro Max with software version 15.2.1 to set up a Watch SE with software 8.3 for a family member (my nine-year-old daughter). I set up a simple, weak passcode just to get it up and running, knowing that with it off my wrist during the setup process, I'd probably be putting it in a lot. Now that it's set up, I want to change it. When I go to Passcode settings on the Watch, the option to change the passcode is grayed out. When I go to the settings in the Watch app on my iPhone, there's no option to change the passcode.