You don't need multiple SIM cards; you can just create new Google accounts. I have my main google account set as the child of a different account and it works great. But the set up was somewhat annoying, took me a couple hours.

I've been postponing writing a guide on how to set this up for a while, but I think I'm motivated to do it now, I'll try to have something up by the 8th here https://tim2othy.github.io/ws/screen-time/, maybe useful for you.