A wees is an orphan. Sometimes you will see the term halfwees [half orphan] or volle wees [full orphan] to refer to a child who lost one or both parents, respectively. While the term wees is nowadays used for a child who lost both parents, in earlier times it could be used for a child who lost one parent. You will see references like “Jan, orphan child of Maria de Wit, assisted by his father Cornelis van Vleuten.”
Before 1811, some parts of the country had a weeskamer [orphan chamber] that oversaw the appointment of guardians and administration of the estate. In other parts of the country, this was overseen by the local court.
After 1811, you can find guardianship appointments in the court records.