yes, good old baking soda and vinegar.
we used an old bottle (and covered it with plastic bags for a mountain feel).
the kids’ expressions are so wonderful. what i am sad about is that my camera battery died on thursday morning. trust me, their expressions were fabulous too (especially the one little girl that i thought was nervous and it turns out she reported she was bored. so bored she couldn’t fall asleep that night. oops.). waiting for things to get started is understandably boring…these kids will be pros.