Using food colouring of primary colours (red, blue and yellow) with the white vinegar will give you the opportunity to talk about the new colours made as the fizzy foam mixes.
THE SCIENCE BIT: Adding the vinegar to the baking soda causes a chemical reaction. During a chemical reaction two ingredients are mixed together and then break apart to form a new substance. Using conditioner makes the reaction last longer.
If you don't have any old squeezy bottles, spooning the vinegar onto the 'snowballs' works just as well, but will probably need a little more grown-up supervision.
Vinegar is an irritant, so be sure to let children know not to squeeze vinegar near their eyes and to use caution when touching with sensitive skin.