Thanks. I just replied on the other thread, I'm looking for the link to that whistle that replaces the sternum strap on a backpack, going to add to theirs when I get them.
We started out with go bags, simple toy backpacks that they would oack some toys in when we traveled to my parents to get them used to carrying stuf with them, then I got my camelbak earlier this year because I got tired of carrying three water bottles and any gear stuffed in my pockets. Wife though it was silly until I showed her a smaller women's pack and how I carried 6x as much water, she always runs out when we are out. We actually wore them to an amusement park this summer to help with the heat
The rest of that album is https://picasaweb.google.com/108192100830485377809/20111023HockingHills# if your interested. Wife wanted to go for a drive and take some fall pictures but I said its so nice we need to get out and walk around a bit.
The map of our adventures here: http://maps.google.com/maps/ms?msid=205129626801920253361.00000112e2f845ffaedf3&msa=0

Here's the one I'm familiar with: Nexus 20mm Airlock Whistle

That's a Canadian retailer, though. You could try looking through the list of distributers at Nexus' site for a seller state-side.

Nexus also has a zipper pull whistle that might be worth looking at too.