Is this refund amount possible?

I can’t help but be nosy about this, but my sister proudly announced that she’d be receiving back 12k this year on her refund.

I told her it sounds like something may have been done incorrectly because neither her nor her husband do additional withholdings. Even if they did I wouldn’t imagine it to be this much.

Just to err on the side of caution I want to tell her to wait before spending that amount for upgrades around the house.

They have two kids as well. I didn’t think the child tax credits worked like that though?

Just curious if a return of this magnitude is even possible given the above.