When logged in to front end, CiviEvent assumes I am registering myself for an event

I am using CiviEvent to allow parents to sign up their children for Sunday school. The event sign up includes a profile with first name, middle name, last name, date of birth, and gender. Everything works fine as long as the end-user/parent is not logged into the front-end. The end-user/parent can enroll 1 or more of their kids for the event.

If they are logged in and go to the sign up form, CiviCRM assumes that they want to register themselves and displays the parent's first name , last name, etc in the form. If the parent replaces their first name with the child's first name then completes the sign up process, then the parent's contact record is updated with the child's name.

For example: Mary Smith is a parent. She wants to sign up her son Tom Smith for Sunday school. If she is logged into the front end, then goes to the Sunday School sign up page, she is presented with her own information in the form:

First Name: Mary
Last Name: Smith
date of birth: Oct 1, 1970
gender: female

So she changes the information to:
First Name: Tom
Last Name: Smith
Date of birth: July 10, 2001
gender: male

and submits the form. Her son Tom is now registered for Sunday School. But Mary's contact record now has first name as "Tom" and gender as male, and date of birth as July 10, 2001.

If she is not logged in, then this problem doesn't occur.