Does a child in Wisconsin have to have their own bedroom or can they share one with their parents?

There are no "bedroom" state laws. Housing associations, apartment complex, government housing may all have rules.

If you are being investigated by Children and Family Services or Child Protection Service you will have to meet their opinions and guidelines.

If you are in a divorce, you are subject to the opinion of the Family Law Judge.

In general, if they are a infant, there should be no issue being in the room with parents.
A older child may use a fold out bed in perhaps the front room or a sofa bed but it is not a good idea to be in same room as parents.