What you describe is almost certainly illegal: Wisconsin law prohibits discriminating against people--such as by not renting to them--based on "family status," which would include having a child. (Here's a link to your state's Equal Rights Division--a webpage about illegal housing discrimination https://dwd.wisconsin.gov/er/civil_rights/housing/housing.htm.) It is also illegal to retain a security deposit unless the tenant owed the landlord money for unpaid rent or damage done to the rental unit. Contact the Equal Rights Division: you may well have a valid legal claim.