Barbies! Read a book, hide n seek, go fish!
What's fun stuff a 15 year old sister can do with her 5 year old sister?
Get a coloring books and crayons , watch a cartoons on t.v., read a book if go for any walks always have another adult with you never go alone unless it's outside in the yard .
Play tag or hid n seek or color with her
Do what ever they want to do
Take her to a G rated movie or Chuckie Cheese . If you live by a park take her there.