It is really remarkable how well CS Lewis was able to write for children given that he had none of his own
The Narnia series is a masterpiece of children's fiction. The chapters are just the right length to read out loud, the tone is perfect for kids, it balances danger with wonder and whimsy
In Narnia, the children sometimes drink alcohol and people occasionally swear, but always with purpose behind it. There is genuine danger and the threat of death is real.
But there are also childhood fantasies of beating up the bully, escaping the evil step-father, and sacrificing for the greater good. The Narnia stories have temptation, transgression, repentance, and absolution in terms that small children can understand.
I'm a father of 3 and I don't think I understand the minds of children as well as CS Lewis did. Even if I weren't a Christian, these are top-tier stories. I'm not sure there is any series that can compare.