Joining Minecraft servers that are public is pretty simple. All you need to do is open your Minecraft launcher and to run the main game, click on play. If you see the main screen on your monitor or device, select the Multiplayer button. You will need to click the button that says Add Server so that you can add a server.
In the box for the Server Name you should type in the name of the server that you want to join. You can find a good list of Minecraft servers or find one that you like from a YouTube video or something. You also have to include the server address on the box that is labeled Server Address. It could be a domain or an IP address. When you are finish with that, click done so that you can add it to your list of servers. Now all you need to do is click on the server that you wish to connect to.
A problem you might encounter though is whitelisting. This means that a server requires you to apply so that your name can be whitelisted on the server. This means, you have the permission to join the server so there is an application process for this. This could include filling out an application form and waiting for the approval which could take hours or days. This might not be the best option if you have an impatient kid but it will give you the assurance that the server admin is familiar with the people in the server. If you and your kid happen to have separate accounts, then you will need to fill out applications for you and your kid. Once you have been added to the whitelist, then you can follow the steps mentioned above.
if you will be joining a non-whitelisted server, then you can simply
join a server by following the steps that have been previously