For your child you get a dependent exemption of $4,050 and if the child is under 17, you get up to $1,000 child tax credit. Neither of those is an amount that you get back.
The dependent exemption reduces your taxable income and thereby reduces your tax, and the child tax credit subtracts directly from your tax, but the ctc is not reundable. You get only enough to reduce your tax to zero or $1,000 maximum.
There is no set amount that you "get back" per child. None.