If that $1900 is his total income for 2016, he wouldn't be required to file a federal return. However, if the W-2G shows federal taxes withheld, your son would have to file a return in order to get them refunded. If he does file, make sure he indicates on his return that someone else can claim him as a dependent. Note that your state filing requirements may be different.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
