If the boys were 16 or over it wasn't illegal. Sixteen is the age of consent in the dictrict.
That's true. It's only a crime in DC if the person is a "child" which is defined as a person who has not yet reached 16 years of age.
While his soliciting a page was entirely inappropriate and rightfully cost him his job, it's not clear yet that he did anything illegal. Foley is a hypocritical prick, that's for sure, but a criminal? Time will tell.
Were the children physically in DC when this happened? Was Foley? If any of the parties involved were over state lines then he did break the law. Using the Internet across state lines to engage in sex with minors (which is declared as 18 in Federal law) is illegal.