A DataTable contains strongly typed Columns [^
], you must declare the Column types when you create it: the default is type is 'string.
Your code shows no information about how you build the collection of DataTables 'tableCollection ... assuming each DataTable is on another Form: the Form with the DropDown needs to have a list of all DataTables bound to the DropDown..
That a main Form creates instances of other Forms does not mean those instances expose
their Controls. I don't like using the word 'Parent for such created instances: the created instances do not "inherit" anything.
Making one Form the 'Parent of another ... by setting the Parent Property of the instance ... is a code practice that is usually a mistake, and will not help you with the issue you describe. A created Form that is 'TopLevel' cannot have a Form 'Parent.
'Parent is often mistakenly thought to refer to olf MDI app architecture.
See the articles OriginalGriff links to in his solution for examples of how to expose contents of one form to another.