My husband and I built a cabin after we were married on some land that he owned prior to our marriage who will own this cabin legally after his death his children or myself?

The cabin became part of the real estate when it was constructed on your husband's individually owned land. Unless he specifically grants that property to you in his will his children may inherit an interest with you under the laws of intestacy in your state. In order to protect your interest, if he wants to do that, he should convey that property to you and himself as tenants by the entirety or as joint tenants with the right of survivorship.