I used to live in Indiana (West Lafayette) and so wrote to a friend there and asked your question.  He knew of no such state-wide rule.  He's going to ask his colleagues at the university if they know of any such rule and if a positive answer comes back, I'll update you here.

You should as the principal this question, too.  It might be a school policy.  We have no such rule here (Silicon Valley, California) and I remember walking my kids to their classroom clearly.

I understand the hesitation to send your kindergartner to class without you on the first day of school.  However, can you imagine if every parent wanted to walk their child down to class?  Considering most classrooms have 22-26 students, that would be more of a distraction for your child and the other children, let alone the teacher who is trying to manage all of the chaos of the first day.  This could also be a liability issue.  Most schools require parents to fill out a background check to make sure all adults should be allowed around children.  I know I wouldn't want an adult in my child's classroom that did not have a background check.  Public schools are far different from Preschool.  You can never be too careful.

The first day of school is usually harder for the kindergarten parents than it is for the children.  Show them confidence and they will follow.