A babysitter one of the examples specifically called out as a household employee in the IRS guidance[1], so if you’re doing it right you should be running payroll. That’s pretty tricky to DIY properly.
For all intents and purposes, a babysitter is looked at just like a nanny in that if they must adhere to the schedule you set and come to your home to take care of your kids based on the rules you set, the IRS will most likely view this as an employment relationship. And taxes can sneak up on you quickly. If the babysitter earns just $15 per hour and works even 10 hours per week, you’ll cross the $2,700 tax withholding threshold in a little over four months.
[1] https://www.care.com/hp/do-you-need-to-pay-taxes-for-your-pa...
And at some point you just pay cash.
Which tells you volumes about the practicality of said law.