How do you talk to children about death?

Let me start by saying that if you have anything rude or nasty to say you can just continue by. My children’s father passed away from an overdose yesterday. They are 6 and 5. How do explain to them about what happened? This is very tragic, and I know he tried to get better for them. We are not together and haven’t been for a few years. They are expecting to stay with him this weekend and I just don’t have the words to tell them that he’s no longer here. If anyone has any advice or links to something I’d greatly appreciate it.

***thank you all for your kind words. I posted this elsewhere and everyone was so rude about it like I had any decision in his choice. You are all so helpful. I really really appreciate it. ❤️