Selfhosted

First you need to understand the difference between Bedrock edition and Java edition. Bedrock is for consoles, phones and Windows, it's the default version that Microsoft pushes now. It's not compatible with Java clients or Java servers. So if you're planning to have the kid play on Switch or something like that, it's not going to work.

Assuming you're clear on all that, you have a few options for Java servers, you can run a plain jane vanilla server (the one that Microsoft provides) fairly easily but it has some limitations, and it's not the most manageable solution. Modded servers are much more capable and flexible but also can be a little more complex in some cases. Overall, I've found Purpur the easiest and most sustainable choice at least a few years ago when I was looking for the right choice it seemed like most people agreed this was the best option. Fabric is another great option, especially if you want to use mods! Fabric has a huge modding ecosystem, second only to Forge.

However I also need to mention that I've got a heavily modded Forge-based server running right now and I really didn't find that any more difficult to set up than any of the others. Even though people usually complain about forge being "difficult" somehow. So take that for what it's worth. I think it doesn't really matter THAT much which server software you use unless you have specific requirements around things like mods, spawn protection, and other kinds of configuration that are probably most useful for large, public servers.

If you do want to run a bedrock server, it gets a little more complicated as you might have to break some things out of the walled garden. I haven't had a lot of success with that but I understand it is possible.