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.
To indicate this, on line 4 of Form 941, check the box marked "If no wages, tips, and other compensation are subject to Social Security or Medicare tax".
If you don't check that box (and skip to line 6), you'll likely receive IRS Notice CP161 which will be a bill indicating you owe Social Security and Medicare taxes for the wages.