If I wanted to play the game “I’m thinking about something that…” and have kids guess what I’m thinking about would I say: “Divine sa m’ap panse…” and “M’ap panse sou yon bagay ki…”? What would be the most natural way to phrase this?

Hi. Although both can be used, the first one gets my mind ready to start guessing....feels more interesting.
And I think you would proceed slightly differently with whichever one you use. For example, if you're thinking about a banana,

Devine sa m’ap panse… li jòn ... li long... li se yon fui...
M’ap panse a yon bagay ki jòn... ki long... ki se yon fui...

 Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words