Use actual food costs (or a reasonable estimate) and enter in the "Other Miscellaneous Business Expense" interview in Business > Business Income and Expenses > Business Expenses. You cannot use "standard per diem meal rates" to calculate meal costs when you are providing the meals directly.
The IRS standard per diem meal rates apply to employee meals while traveling, not when working at their normal place of business. If you choose to feed the child-care providers at your home child-care facility, you have complete control and visibility over meal costs and 'actual cost' is what you are permitted to deduct.
