In addition to above information,
https://www.irs.gov/pub/irs-pdf/p225.pdf
From page 72;
4-H Club or FFA project. If an individual participates in a 4H Club or National FFA Organization (FFA) project, any net income received from sales or prizes related to the project may be subject to income tax. Report the net income as “Other income” on line 21 of Form 1040. If necessary, attach a statement showing the gross income and expenses. The net income may not be subject to SE tax if the project is primarily for educational purposes and not for profit, and is completed by the individual under the rules and economic restrictions of the sponsoring 4H or FFA organization. Such a project is generally not considered a trade or business
This may also apply to you;
You don't report the income in your own name.
If they worked for this money (such as, raised animals and sold them), then each child must file a return in their own name if the net profit (income minus expenses) is more than $400. They will owe self-employment tax on the entire amount and income tax if the amount of net profit is more than $6300. They will need schedule Cs, which is expensive in turbotax online, but they can use the Freedom edition if their income is less than $33,000. It's a separate web site and they would each need their own separate account. https://turbotax.intuit.com/taxfreedom/