A plastic or glass jar
Alka Seltzer tablets
Take a glass jar (approx 1L) and fill approx 1/8 with cold water.
Take the baby oil and fill the jar until nearly full.
Drop a few drops of food colouring into the jar at a time.
Enjoy watching the bubbles of colour slowly sink down and sit at the bottom of the oil layer before slowly melting through and dispersing into the water.
Once you have the water at the desired depth of colour you want, break an Alka Seltzer tablet into quarters and let the fun begin.
And if you really want to get things going, throw a whole tablet in at once....although be prepared for the potential for it to bubble over!
Once you've had enough fun for one day, pop the lid back on, store in the cupboard and bring out again on another day!
And if you don't think it will spoil the surprise, here is the real life action version.
Idea sourced from Meet the Dubiens via Pinterest.