“Hello, my husband is paying child support for two children that we are unsure are his. Where should we start?”
There aren’t really enough facts here to give you a definitive answer. First, how did it happen that he is paying for children if he is not sure that they are his? Is he doing this without a court order, not having gone through the court? Are these children from a prior marriage, or was your husband never married to the mother?
If your husband was married to the woman at the time that the children were conceived and born, he may be out of luck. Many states have laws which mandate that a child conceived and born during a marriage is deemed as a matter of law to be the child of the husband, biological paternity not withstanding.
If the children were born out of wedlock, then I can only surmise that there is no court order, as the first order of business when determining child support for children born out of wedlock is to establish paternity. Either that, or your husband conceded paternity during the proceedings.
If your husband has not otherwise been precluded from challenging paternity either because he was married to the mother and you live in a state with a presumption of marital paternity or because he previously has acknowledged paternity, then in order to determine whether your husband is in fact the father of the children, he will need to file a legal action to establish paternity, through which a DNA paternity test may be ordered by the court.
In any event, a consultation with a family law attorney in your state should tell you your options in short order.