ELI5: What's the difference between a child-key and a hardened child-key in BIP32

[Bitcoin]

ELI5: What's the difference between a child-key and a hardened child-key in BIP32

I've read BIP32, and I do understand it more or less.

Could someone please explain to me like I'm 5 years old what the difference between a child-key and a hardened child-key is?

I'm trying to add HD wallet generation to a service I'm building. I need to be completely informed about this before I dabble in it. Fret not, I'll be using Bitcore, so I won't be dabbling with the crypto directly.

Source: ELI5: What's the difference between a child-key and a hardened child-key in BIP32