Thanks for the help guys.
Just so I am sure I understand correctly, there is no ONE address for a bitcoin core wallet, right? It is all of the receiving addresses we are talking about? Or is there one address?
Which wallet are you talking about?
Bitcoin Core has a tab at the top for "Transactions".
You can click that and see all the transactions that have ever been sent FROM or TO that wallet.
At the bottom is a button that says "Export". If you click that button, you can save the entire list of transactions. You can then open that file with any spreadsheet program, and (with a tiny bit maths that most 11 year olds are capable of) can calculate your balance for any point in time.