I was wondering if there is any internet resource that would tell me who has the advantage in a game of chess if I input the moves? I want to follow my son online in his chess matches but it doesn't mean anything to me and it would be nice to be able to tell how he's doing....
You're looking for a chess engine. A engine can give you the evaluation of the position - a value that relays whether white or black has the advantage. A positive evaluation means white is better - with a greater number indicating a larger advantage - and vice versa.
As for the online resource, there are many options available to you. I would recommend downloading a free graphical user interface client such as XBoard to be used in conjunction with a strong engine, such as Houdini (the free version).
To input the position of your son's game, you can either copy and paste the FEN of the position or the current PGN of the game. The former contains information regarding the position and the latter has the notation of all the moves up to the current position. From there, running the engine will return the evaluation.
There are many tutorials online on how to set up the chess software - here is one example specific to XBoard and Houdini.