I tend to first use the tactic of turning them against their parents. I have a collection of news cuttings of stories of adults who have tortured children. I read these out until the children are adequately distressed and tearful.
I then read out passages from my KJV1611 about hell and point out that this is where their parents want them to go and get them to agree that mummy and daddy are worse than the horrid people in the newspapers.
'Do you think that mummy and daddy can really love you if they don't care if you get hurt real bad?'
Then I read about the glory of heaven where I want them to go.
Then I say 'So who are you going to trust? Naughty mummy and daddy or nice uncle Jack? '
It works every time,
YIC
Jack
Genesis 22:2 And he said, Take now thy son, thine only son Isaac, whom thou lovest, and get thee into the land of Moriah; and offer him there for a burnt offering upon one of the mountains which I will tell thee of.
I know God wouldn't let me believe in Him if He didn't exist.