Employing your minor children in your sole proprietorship can make a lot of sense. It gives them experience, a bit of money, and can lower the average tax rate for your family.
You'll need to have them do "real" work, pay them a reasonable wage, and keep proper records and filings.
One filing you'll need to make is Form 941, "Employer's Quarterly Tax Return". If you ONLY employ your minor children in your sole proprietorship, they won't be subject to Social Security or Medicare taxes.