A city is larger than a town. New York City, Boston, Miami, and Los Angeles are examples of cities. All state or country capitals are cities; cities usually have some significant political, economic or cultural importance. The word town refers to a smaller population center. And a very small population center - even smaller than a town - is called a village.
To complicate things, the central part of a city (especially the main commercial or business area) is called downtown. If you live downtown, you live right in the middle of the main action of the city - and it's more expensive to live downtown than to live in one of the other neighborhoods.
Have your kid help you write an ad for your local newspaper and put signs up around town. Less is more when it comes to effective advertising, so skip the glitter unless your kid feels really strongly about it and make signs using bold markers with your address, the date and time of the sale and an arrow pointing in the right direction.