Hi Kathryn,
In circumstances where a person has children from a different relationship and they die leaving a spouse, the spouse receives a legacy of $350,000 as well as the deceased's personal effects and one-half of the remainder of the deceased's Estate. The deceased's children from former relationship, then share equally in the remaining part of the Estate.
Therefore if the estate was worth more than $350,000 the children should have received their inheritance when he died. If the estate was < $350,000 they do not receive anything. This is why wills are a good idea.
The children are not entitled to receive anything from the spouse's estate.