Hi, I'd like to help you with your question.
Have you taken your toddlers to their doctor yet? You may want to try taking them first to see if there is any evidence of sexual abuse. Keep in mind that doctors are mandated reporters of abuse so if any evidence is found, they will have to report it. But if your child or children have been abused, you will need to report it anyway and the doctor can support you when dealing with the authorities.
Was your husband abused as a child? That might also give you an idea of whether or not it is possible that he is touching your children inappropriately. Adults who are abused as children often repeat the abuse unless they acknowledge their own abuse and get help.
Have you tried talking to your son about who is allowed to touch him? He is a little young yet to grasp the meaning of sexual abuse, but you might be able to talk to him in a general way about what is appropriate and what is not. Do not mention your husband to him, but instead let your son lead the topic. Here are some ideas of how to talk with him:
Ask him open ended questions that require more than a yes or no
Be calm when he answers.
Let him know that he can tell you anything and you will not be mad
Reassure him that if he feels bad about anything or confused, he can tell you
Make sure he knows he is not to blame if something did happen.
You also may want to have your son talk with a counselor. They are trained in helping your child talk about what happens and a therapist can help you determine if there is something going on. Ask your son's doctor for a referral. You can also contact the children's protection services in your area and ask general questions on how you determine sexual abuse.
I hope this has helped you,