Your child knows how to blow bubbles? No? So teach him. Dilute in water and soap or shampoo. Make a wire loop or prepare straws cocktail. Show the child how to blow bubbles. Can be dipped in soapy water with a wire loop and blow into it, and you can omit one end of the straws to blow in the other.
Explain to the child that a straw can only blowing and in any case cannot be drawn in the air. Otherwise in mouth soap, and it is not as tasty as the juice.