I've seen different versions of this on Pinterest and Facebook. I just threw it together from memory.
I took a 9x9 inch baking dish and covered the bottom of the pan with baking soda. I then filled a glass with vinegar and food coloring (first time I did this I did two different colors)I used 2 syringes (that came with our baby Tylenol) I wish I had eye droppers, then this would be something Wyler could do on his own, but he doesn't quite have the finger strength to fill a syringe easily yet. I filled a syringe with the yellow vinegar, passed it to him, and we watch the foaming bubbles as he shot it into the vinegar.
While he emptied one syringe I would fill the other, as he was too excited to wait for me to fill only one, he didn't want to pause the bubble action at all.
After we had emptied the vinegar into the pan he stirred it up with the syringes to get the last of the vinegar and baking soda to react. He would have kept at this activity longer, but he ran out of the baking soda.
Next time I'll use a larger pan, and hopefully have the eye droppers for him to use. And the syringes are going to make an appearance in the bath so he can practice filling them, and strengthening his fingers.