Pebbles and Bam Bam is the best suggestion I've seen thus far. This is something you can only really do successfully with babies. All the other suggestions work pretty fine when the kids are older. Polom & Porom was a pretty awesome suggestion but I doubt anyone up and down the average street would really appreciate it. But if you posted a Polom & Porom photo on the internet it could go viral amongst the cooler gaming sites, if this is something that appeals to you.