2 teaspoons cream of tartar
1 tablespoon oil
Then the colourful foam was just too tempting so it became a glowing bubble-free-for-all and soon became a foamy smooshy bubbly mess :)
Quick aside - I think I've mentioned this before but if you want to do activities that involve straw blowing and not sucking (sometimes difficult for toddlers to master and a mouthful of bubblemix is not that tasty...) then make a little hole in the shaft of the straw. Just doing that makes it pretty much impossible to suck anything up the straw, even if they try!