It depends on how old your son is, but more importantly, how much income he made. The limit changes every year, sorry I don't know what the exact is this year...It has been in the $5,000 range. I read $5700...but of course, please verify and seek professional assistance.
Turbo Tax software programs walk you through that information, so if you do it yourself with one of those, it should still be able to legally guide you. Don't know the details, but turbo tax is advertising free filing on line so it's worth checking out.