This is a great activity for toddlers/preschoolers (or really any kid who likes bubbles). It was easy to make and also worked as a fantastic learning tool as we were able to experiment with mixing colours.
Using the handheld mixer, mix 2 tbsp of dish soap with 1/4 cup of water in a bowl. It will take about 2 minutes for the foam to form, at this point you can mix in some food colouring. Scoop out the foam and dump it in your “sensory bin”. For each colour I mixed two batches of the foam. The 1/4 cup of water and 2 tbsp of dish soap actually make quite a bit. I do suggest using this as soon as possible to avoid the bubbles from disappearing.