We had Miss M's birthday party today and it was a roaring (if exhausting for Mama) success. I'm especially pleased that the snow globes worked out properly :-)
I added about a teaspoon of Glycerin [after a long hunt we finally found it at our local craft store in the baking department -- drug stores do not carry this in the US anymore], and filled the bottles to the rim with water. For the kids who chose creatures that needed to be hot-glued to the lid, rather than swimmers, I filled the bottles a bit less than full.
To seal the bottles I squeezed out a ribbon of hot glue all the way around the inside of the lids before sealing tightly. A few of the snow globes didn't seal as well as expected (I called these The Leakers), so I sealed the outer rim of the lid with another ribbon of hot glue. This isn't as pretty, but it works.
I'd done a trial run a few days ago that didn't go as well. If you want to know what not to do, read this.
>> Update Nov.30th, 2006: The folks at Kiddley have posted a slightly different take on this today. I like the idea of trying superglue instead of using the ol' hot glue gun.
>> Update Dec.5th, 2007: Martha Stewart also has this project up online with a Christmas theme.
>> Update Nov. 22nd, 2008: Gretchen over at Cocktail Mom's had the inspired idea to use Aquarium sealer with great success. I'm going to try that next time because I think that will have a more permanent seal.