I don't think a 10 year old kid will understand blockchain technology because an adult person can't even understand blockchain so how come a kid will understand it?
A 10-year old kid doesn't have enough knowledge about technology and it's advancement (unless he's so genius or gifted for his age). They mostly spend their time playing online games like playing Minecraft. But, they wouldn't be interested in any blockchain-related things.
But if you want to explain it to a kid, give him the lightest explanation. It doesn't have to be that specific or more on technicalities. You can simply say, it's a kind of technological advancement that will be part of our future. It can help a lot of people to makes things easier for them to do. You can example a robot. Robot helps people to do things easily. While blockchain is like a robot who can help in making things easier with the use of this technology.
They're too young to be thinking such complicated things. So it's better to wait for a kid to mature before explaining it further. Or you could just explain it to him from the simplest way and then make sure he will often encounter than word so he can keep it in his mind and wouldn't forget about it.
I remember the time when Minecraft had servers you could earn Bitcoin on by just playing and destroying blocks.
A child growing up WITH the blockchain technology would make it easy-peasy when they are 18+ to use it. I grew up as a child interested in about anything related to tech, and today it's easy to understand most things about it.. and that's the perfect example I can give. I grew up with English video games, movies and forums and today I am a fluent English speaker. It helps a lot.
There's no way you can explain cryptocurrencies to a child without getting him confused with every single sentence you speak. As I said earlier, practice is the best way to do it. Give a kid a Minecraft premium account, a server that integrates a cryptocurrency as the in-game economy and a wallet for the cryptocurrency. I guarantee in max 1 year he will know what cryptocurrencies are and how they work.