Basic accounting principles are essential to understand how a business actually operates. However, so much of the content available is geared at adults looking to go into accounting as a career. This page does a nice job of defining and explaining basic accounting principles in a way that is accessible to young students.
The National Accounting for Kids Day facilitates young children learning about accounting. They provide resources and group activities to get kids involved in learning more about accounting through this activity. Use the drop-down menu to choose your state for specific resources and information.
Alan the Accountant is a great iPhone app book to interest kids in accounting. The level of instructional detail in the book isn't in-depth, but it does a good job showing students what it means to have a career in accounting.
Economics and finance are an essential part of business. I specifically like this lesson for the activity questions at the bottom of the page that help students apply these concepts to a real world business.
This video describes how Cost of Goods Sold (COGS) are determined for a manufacturing business. While we frequently talk about how COGS take place in a service company (think the classic lemonade stand business), going more into depth about actually creating a product isn't as frequently discussed. This example is great for students to understand the basic concepts and want to apply it in a more complex example.