You must actually pay someone to care for your child. If they work in your home and you pay them more than $2200, you must issue a W-2 and pay household employee tax. You must report their name and SSN on your tax return, and the IRS will be looking for a tax return in their name that reports the taxable income.
In addition, the person you pay to watch your child can't be your spouse, your dependent, or the other parent of your child.
While it is technically legal for you to claim the credit if you pay your live-in romantic partner to care for child so you can work, the household employee tax you must pay on their salary will negate most or all of the credit benefit. (Household employee tax is 15% of the wages, the childcare credit is between 20%-35% of the first $3000 of expenses. So if you paid your partner more than $4000, the credit to you will be less than the household employee tax you must pay.)
If this is your partners only income, they probably won't pay income tax, but the arrangement may have implications for any income-based benefits your partner is receiving.
