If a child is likely to have a life full of pain and suffering is that a reason against bringing the child into existence? - yes.
If a child is likely to have a happy, healthy life, is that a reason for bringing the child into existence? - yes(for pessimists – "Let's say yes"). Can we produce only happy people? - no. 

How can we justify continuance of our species in the face of our knowledge that it will certainly bring suffering to innocent future human beings, without accepting unlimited utilitarism? There is no way to bring happy people into existence and not to bringing atlast some unhappy people into existence.