Salve,
Welcome to the forum. As you and your son have just started Latin, I would like to make you aware of the Latin textbook from which I am learning. The series is called "Lingua Latina", written by a Danish author, Hans H. Ørberg. The intriguing thing about Ørberg's method is that both of the main texts - "Familia Romana" and "Roma Aeterna" are written entirely in graded Latin. It starts from the very beginning, assuming absolutely no knowledge of Latin vocabulary or grammar at all, and slowly builds the reader's vocabulary and grammatical knowledge as he or she progresses through its pages. New vocabulary is taught through the word's repetition in various different contexts. Any words which are difficult to explain in context are either illustrated through pictures in the margin, or through short and easy to understand explanations in Latin. I am working through the first main text of the series, Familia Romana, and absolutely love it! I'll put a few links below so you can see how the book approaches Latin. Although I find this approach absolutely ideal, I realise that it's certainly not for everyone!
http://pullins.com/txt/LinguaLatina.htm#set_1 - this is the section of the publisher's webpage explaining Lingua Latina and the other books in the series. Unfortunately, I believe that only the two main texts are
entirely in Latin.
http://www.lingua-latina.dk/index2.htm - This is the very first page of the first main text. To look at other sample pages, there's a link to the left of the Latin text. If you are unable to work out the meaning of a word from context, you can either buy the word lists from pullins or download them free from the first page I linked.
Fortuna tecum sit - good luck. I hope some of this information is of help to you and your son. If you don't decide to go for Lingua Latina, then good luck with D'Ooge. I downloaded that before my copy of Lingua Latina arrived, and found it to be very useful. Also, if you decide to go for Lingua Latina, then I would advise not using Amazon, but using the publisher's website. I cannot comment on amazon.com, but UK amazon took a very long time to deliver my copy of the main text. I have heard that other people have experienced the same problem, too.
Again, hope that was of some use. Good luck.
Jack