Here's a fun way to keep your child actively engaged while you're making dinner (folding laundry, feeding baby #2...).
This is what you need: placemat, paper towels, bowl, dirty pennies, old toothbrush, vinegar & salt (or warm water and soap for younger ones)
Preface this activity with an explanation about how coins are very dirty because they are constantly passed from person to person. The copper (the outside of the penny) becomes tarnished (the dull, greenish color is formed from copper oxide). The acid from the vinegar dissolves the copper oxide and leaves behind shiny pennies. We had fun dunking the penny halfway into the solution. Experiment with your little scientist! Try lemon juice too- it smells better!