Under the Wages & Income  tab select the "Explore On My Own" option (if presented)

Then scroll down to Business Items and elect to start/update Business Income & Expenses (SCH C)

If you had "any" income from babysitting regardless of the amount, and you do NOT receive a W-2 for that income, you are considered to be self-employed as far as the IRS is concerned, and you need to report that income. You are allowed to deduct your babysitting related expenses from that income to arrive at the net income from babysitting. If the net income is more than $400, only then will you also pay the additional Self-Employment tax