The fact that they listed it after telling you it was rented is likely enough to warrant an investigation. You can call and talk to an intake person and they can help you determine whether there is enough cause. Worst case scenario, they call the landlord and do not have enough there to file a complaint - but he will be unlikely to deny tenants based on children ever again!

Because I am a nosey parker posey, I totally looked up the on-line complaint process: http://www.hum.wa.gov/CQ/index.html

Cause I am a geek for process.