If you know someone who has lost a child please don't tell them it will be okay. It's never going to be okay for that child to not be here. Don't remind them that God has a plan. They probably know that, but right now there is no way to understand what plan might include the loss of their child.
Don't tell them it will get easier. I don't want it to ever get easy to miss my son.
We know you care and you don't know what to say but a hug and no word is better than some of the phrases people feel they need to say.