I have already found this answer but forgot I had posted here. If memory serves me correctly stepchildren are far down the list for intestate distribtution in Iowa, following the decedent's natural children (issue, as they are called), the decedent's parents, the decedent's brothers and sisters, etc., etc.
The stepchildren's time to step forward would have been when their natural parent, spouse of the decedent, passed away. If their natural parent had died intestate also, half the estate would have gone to them and the other half to the surviving spouse, to be passed on to their natural children, etc., at their death.
In the particular case I was inquiring about both parents had poorly drawn wills that easily could have proven defective.