There is a concept highly pushed in conservative Christianity, and that is the Age of Accountability. Through no particular Biblical text -- mostly just sane but partial logic -- someone down the authority chain decided that there was a maximum age past which people suddenly become accountable for their sins. I will refer to it as the AoA for sanity's sake, because Accountability is a huge word. The AoA is loosely defined as the point where a person has enough understanding of what is right and wrong to make good decisions and do what is right.
Very little kids clearly have no particular clue. They scream, hit, steal, whatever they want, they try to get. They have no reasonable concept of "moral" or "ethical" or whatever. They know they have needs, and they try to take the most direct path between the need and the fulfilling thereof. You can't really blame them for that, because they're underdeveloped and don't have the knowledge and brain maturity to do otherwise.
The AoA, despite its general definition, is often set at age 12. Why? No other reason than Jesus began showing consciously executed signs of divine knowledge at 12, according to text. We don't actually know if Jesus started exhibiting divinity before that, but the first recorded moment is when Mary and Joseph, through some mishap we don't know, lose Jesus while heading home and have to turn back and search for the missing child. They find Jesus in a synagogue, astounding the local teachers with His knowledge. Beforehand, obviously, there were the singing Christmas angels and whatnot, but this was the first voluntary action we see Jesus taking that is "superhuman." Never mind the fact that Jesus was clearly incredibly mature for His age as a human, and that He had a huge bank of knowledge that no one else could possibly have access to, the AoA is set at 12 from this story.
Ergo, according to Christian lore, at age 12, every human being now has the ability to damn himself.
Okay, when I was a kid, this scared the pants off me, I don't know about you. The moment my 12th birthday hit, it was like a huge weight came down around my shoulders. I now had Responsibility. I didn't ask for it. I certainly didn't want it. Who wants the chance to screw up their eternal fate?
And, in complete, unashamed seriousness, I would much rather die than have that opportunity.
This leads back to eternal Hell. If Hell is permanent, and your state of belief on Earth can screw you forever -- especially if by some shadow of a chance I've done it wrong and some other religion with a Hell figure is correct -- then I would much rather have been killed as a baby when I had no opportunity to ruin it for myself.
Even when you include religious mandate, what is God trying to get at when He gives us commandments? Love your neighbor. Treat him well. Do good to him. Be a nice person.
What is the nice thing to do, when someone is faced with the opportunity to completely destroy their fate? What is the only way to help them?
It's the same thing we do to wounded animals. We kill them. No fancy words -- that's exactly what we do. When the animal is faced with dire suffering, instead of letting it be tortured into oblivion, we do the kindhearted thing and end its life. This is considered humane, moral, and correct. Now this creature is at peace. So, when the difference is between heaven and even the slightest possibility of permanent Hell, the solution is very, direly, simple.
Kill every single human being before their 12th birthday. End the human race in a couple of generations. Everyone goes to Heaven and the world ends for us. This is is the only humane option for us.
There is one contingency plan, if you allow for those who have never heard of Jesus to go to Heaven. This is a big if for some people. If you consider that tenet, the other solution is to completely eliminate Christianity. By eradicating the very religion that is trying to promote salvation, you prevent anyone from losing salvation by gaining knowledge and then choosing to ignore it. If those who never hear, are considered to never have had a chance, then we should never give anyone a chance. The worst life on Earth, even a spiritually unfulfilled and miserable one, is infinitely greater than eternal torture.
When your most humane options become "murder the entire human race" and "eliminate your own religious system," something is incredibly, direly wrong.
And besides, what happens if someone is precocious? What if their brain develops fast and they gain moral understanding at age 10? The age-12 rule is silly and has no real basis in reality or Scripture, while you could argue for a moving AoA due to "innocents going to heaven." The mentally unstable or impaired may not even have an AoA. So in the end, it's a huge crapshoot as to when someone gets the chance to go to permanent Hell, when you have this moving target. Or what happens if someone dies at age 13, after having just a year -- and a year during adolescence, when people make crap decisions and are biologically screwed with regards to good sense -- to sort their entire lives out?