What would be the best way to make a treasure map?

I am planning a boating trip with several kids this summer and I am wondering how I could make a good treasure map and treasure box for ten year old kids?
My plan is to bury the treasure ahead of time and then give the kids the map and tell them to find the treasure and they have to jump off boat and swim ashore.
Much like I seen in a movie years ago call White Squall,, which is probably the best boating movie ever.
Thank you for your help!

Get really nice parchment from a craft store and stain it with tea. burn the edges a little.

Get a nice ink pen to draw the map. (the kind you fill yourself)

Try to come up with riddles to the next spot too. That would be fun.

♥Crazy bratz kidz:A quest to find treasure♥