Deductions & credits

All of you guys are very helpful. 

However, I am still not understanding why we are not getting the full credit for our children.

I am sorry I don't really understand all the tax terminologies. 

If I heard you correctly , we are not getting the credit because of our income since we are self employee.

If we were W2 workers then the credit will apply to us. Also the credit in non refundable but used to offset tax due for normal income?

Also that credit can not be used to offset the FICA due because it is handle differently. 

So now we end up with a bill and nothing after all the struggle we went through last year.

What can we do differently this year?