I think this is a tough one because table top often involves reading, writing, and mathematics that a 5 year old might not be able to handle. My 11 year old niece is getting into D&D now, but when she was 5, she would not have had the wherewithal to play.

When she was 5, though, she did enjoy collaborative storytelling. I would start by building the character with her:

"Once upon a time there was a..."

"Squirrel!"

"Yeah, and this squirrel was named..."

"Elsa!"

Then, when we'd established the character she wanted, we'd establish the type of "campaign" she wanted:

"So, one day Elsa the Queen of Purple Squirrel Kingdom was sitting on her throne when one of her squirrel subjects came to ask her for help, 'Please, O wise Queen, I need your help...'"

"Finding Taylor Swift!"

Then we'd proceed to tell the story of how Queen Elsa the Squirrel saved Taylor Swift from the next door neighbor's dog together (actual example), stopping every few sentences to get her input.

I learned to play this game with her from her father, who also happens to be a great D&D GM.