If you, or your son, plan on using the phone for so much, I would really suggest getting yourself a plan with either unlimited data, or one that doesn't cut off when you hit the limit. Some companies will just drop your speed down to 3g or 2g when you hit the limit, and not charge more.
You might want to look into that.
Additionally, if a lot of this usage is while at home, or while you have access to WiFi, then turn off your data when in such locations and access everything via WiFi. I do it all the time.