It can be terrifying if you suspect abuse at your ex's home. Here are some steps to navigate what is a very delicate situation:
Contact a lawyer. If you have a lawyer, call him and get some legal advice. If you don't have an attorney, find a good one. Local child protection agencies may react differently to abuse accusations from one state to another. Your lawyer will know your local situation.
Be certain. Proving child abuse is no simple matter. Consider this possibility: Suppose your children do show evidence of abuse, but will not, for their own reasons, incriminate your ex. You may become suspect! If so, your children will be removed from your home until the culprit can be determined. Many times ex-spouses are accused unjustly during custody battles. Judges are at a loss to do anything unless they have hard evidence.
Be prepared to prove your suspicions. If you try and fail the first time, proof will become more and more difficult to get in the future. You cannot withhold visitation when the court has established it. So whatever you do, don't refuse to let the children visit your ex, or you may be found in contempt. These are the reasons you call your lawyer the instant you suspect abuse.
When you are certain: If you can prove abuse, move as quickly as possible to prevent it from happening again. You might even want to call your local child protection agency yourself. Do not be surprised if your claims are met with some initial skepticism. Agencies get this kind of accusation often from vindictive ex-spouses. Don't give up though — your children's best interests are at heart.