What does it mean to be a kid at heart?
That is hard as there are two ways to look at it and one way can be negative the other positive.
One way I look at it is a kid at heart will be childlike. That will mean taking enjoyment in the small stuff as well as having an innocent outlook on life.
The negative version is childish which is showing how a kid can sometimes react which is to act immature which can be hurtful to others.
I prefer the first version as it allows me to see the wonders of the world from a different standpoint and not be destroyed by what is happening in the world.
Crazy Canadian Writing 