How was Carrie able to sign Milo out of school?

Sorry if this has already been posted, but how on earth was Carrie allowed to pick up Milo from school? It certainly couldn’t have been based on a fake after-school playdate text. The only thing I could think of is that Carrie had helped Milo’s nanny with the initial school paperwork form and had possibly put her own name down as being an authorized person?