I did a better job cutting the bottles this time. Then I grabbed two light weight wash clothes and secured one around each end of the bottles with a rubber band. Then I poured some Dawn dish washing liquid in a bowl with a little water, swirled it around with my finger and the girls lightly dipped the washcloth end of the bottles in the bowl.
Then they started blowing in the bottles and this is what they got:
Just make sure you tell your kids to blow out only and not to breathe back in. Sarah learned this the hard way and once she got a mouthful of bubbles, she was over the whole thing.