Do my kids get property that there dad had before he remarried

Whether or not your children have rights to their dad's property, would depend upon whether or not Dad had a will or not.  If he had a will and it was probated, my guess is that he probably left everything to his new wife.  If not, depending on the family tree, your children could be entitled to a share of the property.  Either way someone has to go to court (Probate Court) to have the heirs determined if there is no will.