You should speak with an attorney--you may have a cause of action, to recover what you paid the exterminator, your other costs, and possible for any medical care that might be prudent for you or your children. If he deliberately lied to you, then he committed fraud, which is something you can sue for. If he didn't lie, but was unreasonably careless or even reckless, or not sufficiently trained or knowledgeable for the job he voluntarily took on, he might have been negligent.Alternatively, if you think the total costs you might try to claim for are not enough to justify an attorney--and usually, you need at least $1,500 or so to make it worthwhile (rough rule of thumb, subject to many variables), you could try to bring a claim in small claims court. However, I'd recommend at least speaking with a lawyer first (many provide a free initial consultation)--if, under a  more detailed analsys of the situation, the exterminator violated pesticide-related laws, violated some consumer protection law, or acted SO recklessly or intentionally bad that punitive damages might be possible, the amount you might be able to sue for could be larger. Good luck.