The Loeb is probably the only English/Latin language version. But as Hylander points out the English version is over a hundred years old.
James O’Donnell has made a new translation and I can thoroughly recommend it. There is a discussion here which unfortunately goes off the rails. http://discourse.textkit.com/t/how-to-read-caesar/17686/1
Is your son reading Caesar in class? Unless his latin is quite advanced he might find it a challenge. Although some passages are set for intermediate students, trying to read the whole thing is not easy. There is an excellent if rather old commentary here https://archive.org/details/CaesarsGallicWarKelsey/mode/2up by Kelsey. Its age is mitigated by the extensive notes and grammatical help. Your son might find the illustrations attractive. I still do!
Edit: this is a later version which has more grammatical help: https://archive.org/details/ciuliicaesarisco00caesrich/page/n7/mode/2up