Children who are no longer active in your center should be graduated (click here to see how to graduate a child).
Once a child is graduated, here is how you find their profile:
Educators, simply tap on the 4th menu item along the top of the screen (looks like a sign post) and select "Graduated".
Administrators, your menu is different and you can find graduated children by going to a classroom, scrolling to the bottom of the page, and selecting "Enrollment". Scroll to the bottom of the Enrollment page to see a list of graduated children.