Planning Dash's 8th Birthday: a Scavenger hunt?

For Dash's eighth birthday party, we're doing our usual backyard party with barbecue and moonbounce, but this year Dash asked for a scavenger hunt. I can't remember getting involved with scavenger hunts when I was younger outside of organized events at camp with kids I barely knew. I know there is a subculture of people who are passionate about it, geocaching items worldwide for others to find. 

While I can't imagine parents being okay with their 8 year olds wandering the neighborhood, looking for random stuff, would they be okay with going down to the creek to do a nature scavenger hunt? Here is a suggested list for a nature hunt, from http://www.birthdaypartyideas4kids.com:

1.  2 different types of grass

2.  Leaves from 3 different trees

3.  Large rock

4.  Moss

5.  3 different colored smooth stones

6.  Berry

7.  Pinecone

8.  Something plastic (explain how it doesn't belong in nature)

9.  Water reed

10. Animal tracks (draw them on paper after you find them)

11. Nut or acorn

12. Flower

13. Something red

14. Feather

16. Seeds

17. Wood

18. Stick

19. Something that fell out of a tree

20. Something that begins with the first letter of the birthday child's name

We could potentially do this in our back yard, but the creek is just across the street and I would go them, if parents agreed. Of course, I'll need to check with Dash to find out what he had in mind!