Without the CTC, you would have a tax liability and could potentially owe. There are 2 credits - one is Child Tax Credit and the other is Additional Child Tax Credit. The first one is nonrefundable and reduces your tax liability. The second one is refundable up to $1600 each depending on how much of the first credit was used to reduce your tax liability. These credits are for children under 17.
There is a bill in Congress that if signed into law will affect your tax return. Learn more here.