₪₪₪ Why does the IRS give some people a bigger refund than they paid?

Can someone explain how the IRS can give a refund(definition. Return of payment) in excess of the amount someone has paid in taxes. And furthermore, why don’t they consider that as income?

And along the same lines, why do people without children not get a credit for not adding to the tax burden of society?

Not a soap box, I just would like someone to explain the tax laws.