Now to organize pictures for the hunt -- question about the hunt....do I make the kids separate so they can each "experience" finding? Or just let them go together? I still don't know exact numbers, it's not too big, probably about 10 kids.
I was thinking of having a picture for them to color of a pirate ship on a paper goody bag when they arrive and then they take that bag around with them on their treasure hunt collecting their prizes....
HMMMM....at that age.....I would have them work together for the hunt. Some may be more adept at figuring things out then others and would feel lost. kinda hard to describe but I think you know what I mean. Let's see how to explain and do so all can participate equally.......think think think..... OK how is this (and mind you it is 5 something in the morning) Put each clue in an envelope or maybe roll the paper up like a scroll and tie (I like that better more noticible) Then as they find the clue in that area they can hand it to the adult in charge to unroll and show to them so they can find next one. Does that make any sense? Like I said 5AM.

You can even make a big deal out of finding each one by being in character. "ARRRG Matey, You be finding another clue!"

There's that 5AM thing again. For each clue you can hold it up to show them as a group and say who knows what this is? Then they can all go look at once when you give the signal. I wouldnt do more then 3-5 clues.
Not sure what you are planning on using as the treasure, but dont forget to have an X marks the spot. If you are using a pool filled with sand with tiny toys have little shovels they can dig with (as long as it is not in your living room...LOL) If it is, what about a pile of pillows covered with a blanket with a big X made out of paper on top. This would be the good place to put the treat bags. Just make it clear to them that they get one treasure each.You could even make them find the one with their name on it. And make them all the same. If you use the treat bags, I would make this the last activity chase them out the door as soon as possible--saves on having them open the bags (tell them they cant open their treasure till they get home)and losing most of the stuff out of them. SEAL THEM WELL!
NEXT....
Coloring pages...YES. Carrying around goodie bags, NO. At that age they are too young to be responsible for their belongings in an exciting situation and you will be pounded with the question of MS. GOTTA where did I put my bag? OR. MS GOTTA, he has my bag. Trust me much less stressful on you. If you need something to put small things in as they collect them, use ziploc sandwich bags with their name on them. Have one adult responsible for them and tell the kids that each time they accrue something to go give it to MR. WHATSHISNAME
Other ideas for beginning activity...let them play tic tac toe on paper. Fits in with the x marks the spot theme. THey will probably not want to stop playing.

OK now it is 6AM and the ideas are still flowing...LOL GOD I wish I could sleep.
The reason I say to avoid whining situations is that I always hated the parties as a kid where one child won all the prizes or you lost most of you goody bag stuff before you even left the party. Had years of parties for my older DD and never had a problem with whining for the fact I circumvented it before it started. When they hit around 9 or so then it becomes easier. Good luck again.
BTW..the kids in your sig pic are cuties.