Why my children taxes are only 512.00

If you are asking about your child tax credit if the amount is $512, then it is likely you only had $512 in tax liability.  The child tax credit is a non-refundable credit. This means, you can only get as much as you owe in taxes.  Once your balance is $0, you can't claim more than that.

However, if it is possible then to get the Additional Child Tax Credit which is refundable.  If this amount was only $512, it is because your income limited the credit.  This credit is calculated by taking your earned income and subtracting $2,500 then multiplying it by 15%.  The credit is then limited to the lower of that number or $1,700 which is the maximum amount for the additional child tax credit. 

What is the Additional Child Tax Credit?