Welcome!
There is a ton of info you can find in the Do It Yourself (DIY) section if you are interested in having your kid do some fun projects. Plus it helps you learn about the biological cycle of the tank and much more.
Just some basics on what to know is that if and when you get a tank, you need to let the tank's water cycle, a creation and balancing of bacteria through the water, sand, rock. Then you are ready for some fish and if you want to get into coral, you will need some correct lighting which you can find for sale on here or many other sites pretty cheap.
In this hobby though, you must have patients. Rushing will usually lead to a disaster. There are some charts around of fish compatability. If you are wanting to go with some coral, pay attention to those that are reef safe as not all are.
There are plenty of us on here willing to help out in any form that we can. We also have meetings once a month to get to gether, eat, talk, etc. Helps put some faces to some names and usually a better form of getting an understanding of a subject that you may not understand.
If you need to get anything, check with some sponsors, they can usually get you some deals.