Second Marriage Having Child But Not Informed To The Wife

My brother got divorced and having a son (age 7) living separately with grandmother in different city. Now married to another girl (She is also Divorcee) through matrimonial website register. Having child is mentioned in the profile, but after the marriage now my brother wife claiming that they were not aware that my brother holds a child. Both the family not discussed too much about the first marriage in from both side. Just discussed blankly that no need to consider about the first marriage whatever good or bad. Child is also living only with his grandmother. Is this an offence.. How to deal with this. Moreover, we don't have any personal motive or intention to hide this from the bride family. Neither they asked any question about this and nor we didn't express or questioned about their first marriage. Please advice.