I think I’m going to be pretty much verboten to say anything about my beliefs to my little nieces. Ever. (My parents and I have been already stringently warned that we are not to say anything positive in favor of evolution around those girls, either, ever.)
But, I currently think the best way to teach kids about this is to use comparisons like these (some of which I use in my fictional novels, by the way–others are taken more-or-less directly from the OT and the NT):
1.) some kids, when they can’t get their way, hold their breath until they pass out, in order to grieve their parents. It hurts very much to hold one’s breath, the longer they do it; but still, some kids are so insistent on doing what is wrong, that they can actually manage to hold their breath until they pass out!
The pain they feel, however, is trying to tell them that something is wrong, and that they need to stop doing what they’re doing and breathe, because they’re hurting themselves. And when they eventually pass out, that’s their body’s way of keeping them from hurting themselves too much–the first result of which is that they start to breathe again!
Even though parents who love their children are hurt even more by a child who is holding her breath than the child (which is precisely why the child is holding her breath!), nevertheless the best thing for the child may be for the parent to just bear the pain with her until she has to give up and passes out and starts to breathe again. After which, maybe she’ll learn a lesson about trying to do that!
Although, neither is there any guarantee that she’ll put that lesson she’s learned to good use, either.
2.) God wants us to play nice with other kids, whether our age or younger or older, and to love our parents; and if we refuse to do that, we’ll get a stern talking too, and maybe even a spanking, and be sent to our room for a while with the lights out and with nothing fun in there. God keeps checking in on us, to see if we’re ready to come out now and play nice with other kids. (Lots of OT prophecies about Israel amount to this, including the announcement from Isaiah read by Jesus at the beginning of His ministry in Nazareth.) If we decide we’ll just not ever leave our room again, God will turn up the heat on us, to make us come out. Grownups can take a lot more of God’s kind of heat, so God uses more on us, if He has to. It isn’t really fire, but that’s how it’s pictured in the Bible, because for a lot of people it’s easier to think about it like that.
3.) God spanks us in various ways so that we’ll be sorry for doing things wrong, but it’s because He loves us. The spanking hurts Him more than it does us, and it goes on hurting Him forever and ever, even after we’ve put it all behind us. But He loves us, and wants us to be good, so He gladly bears that pain for us. When Jesus is up on the cross, that’s God’s way of showing that He shares our spankings with us. (Among other things. There are several things Jesus is doing on the cross, but that’s one of them, too.)
4.) God’s love is so strong that it feels like fire, sooner or later, when we insist on being bad. God is salting us with His love, though, even when it feels like fire, so that we’ll be stronger and taste better and be more healthy to other people. God salts everyone this way and for this purpose. And the fire He uses is Himself, as the Holy Spirit. (Basically Mark 9:49-50) When we’re good it feels great. When we’re sick, it may or may not feel so great, like sometimes when you’re sick a cuddle feels good but a shot doesn’t feel so good, but both of them help you get better, but even when you’re cuddling you still feel sick, until you get better. When we’re trying to be bad and unhealthy and sick, however, God’s love for us may feel pretty sharp.
5.) God’s fire is like eating a pizza. When you’re healthy and good, it feels great. When you’re sick with a sore throat, you still need to eat, and a pizza (or applesauce or whatever) may still taste good, or your taste may be off because you’re sick, but going down your sore throat it always tends to hurt even if it tastes good. If you refuse to eat, however, your hunger hurts much worse than a sore throat; and in order to keep you alive, so you’ll get better again, they might even stick needles and tubes in you. Which is far from fun, even though they’re trying to help you to live and get better. The doctor won’t give up trying to help you that way, either, until you’re well again. Neither does God, when He’s trying to help us get better.
6.) Hot water can hurt sometimes; and when you’re really dirty, you may need lots of hot water. If we insist on being dirty all the time, though… well…! God isn’t going to stop trying to wash us clean. That’s because He loves us and wants us to be clean and healthy. When Jesus sends the goats away, they’re going away for some brisk cleaning from God–that’s what it says in the original language. They’ll be all right eventually, if they’ll learn not to keep going out and getting themselves dirty with sin and selfishness. So long as they do that, though, God will keep on scrubbing them–even when the soap gets in their eyes, sometimes. What He’s scrubbing them with is His love, which is kind of like hot chocolate; we’re really supposed to drink it!
6.5.) You know how cats hate to be washed, and scratch us, but they still need to be washed sometimes? The cat might yowl that she’s “in hell”; God puts up with our scratches because He loves us and knows we still need to be washed sometimes, more than we can wash ourselves.
7.) When a person’s body gets too cold, and they’re in danger of freezing to death, it doesn’t feel to them like they’re in danger. They feel warm and sleepy instead, and they don’t want to move, only fall asleep. But in order to live, they have to move and be warmed up. The problem with this, is that their body may have already fallen asleep, like when you sit on your leg or arm wrong and it goes numb. Then when you start walking around it really really really HURTS!!–like being stabbed with needles of fire. But it’s the only way to get better, and to save your arm or leg. Trying to save someone who is freezing to death is difficult, because their whole body has become like that, so warming up and moving around and getting life to the nerves again, feels like being stung all over–while freezing to death feels all warm and comfy and sleepy! In hell, God is trying to keep people from freezing to death by giving them life, but they’re already so far gone it feels like being stung all over with fire. The longer they keep trying to freeze to death, though, the longer it’s going to hurt.
8.) Sometimes, grownups go out to fight against God with thorns and thistles. They think that they can hurt God this way, although the thorns and thistles are actually hurting them! So, God burns up the thorns and thistles–which burns those grownups, too, so long as they keep on trying to hold the thorns and thistles. If they throw them away, and hug God instead of trying to hit Him with thorns and thistles, they will discover that He is their friend and that He doesn’t hate them after all–just as He was trying to tell them He didn’t. (This illustration is taken directly from a paragraph in Isaiah.)
9.) “Sometimes a bone that has been broken, by foolishness or by fate, heals wrongly, crippling the shape and the function, destroying the joy that could be had, that still could be had again… if only the bone can be rebroken, and properly set to heal.
"But, it hurts to break a bone. And it hurts, beyond comprehension, beyond the bearing of consciousness, to break a bone that has badly been set, swollen with infection… infection that sooner or later will spread to corrupt and destroy.
"It hurts so badly sometimes to heal, that only trust will allow the healing to start.
“And no broken bone can be rightly rebroken and set, without some co-operation, some willingness to face the pain, some willingness to find someone to trust, some willingness to take such a risk.
“How much harder it is to heal, when one’s self is what has been broken… by foolishness or by fate…”
(That’s something for an older child, maybe; also a quote from a character in my novel Edge of Justice, which I’m supposed to be working on editing right now… 
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Maybe those will be helpful. But your daughter is still going to be confused when she hears other people saying that God sends kids to their room, then walls them up and sets fire to the room before abandoning them forever. 
