Rather than worrying about building a list of topics, you should work on creating a framework to process what he learns in school and ask questions that lead to important knowledge.

http://historicalthinking.ca/historical-thinking-concepts

This is the framework we have started using in Ontario, and I find it extremely valuable. I teach grade 7 history, and find that teaching these skills helps get us away from the Great Men model of history in education.

A little late to the party, but as an avid self-taught history buff, I figured I'd through my $0.02 in. While I absolutely agree with the framework concept, to answer your original question - there are a few historical themes I would focus on:

• Texas History: (duh!) I found that 7th grade Texas history is far too basic, and I had to delve into the subject in my off time.
• WWI/WWII History: Being a soldier, I feel I have to include it in the list
• French Revolution/Enlightenment: The Founding Fathers were heavily influenced by European enlightenment thinking, and I found that studying European history from the time, helps better understand where we came from