A vondeling is a foundling, an abandoned child whose parents are unknown. It was rare for children to be abandoned. Most cases where children were abandoned took place in the city, not in the countryside. Most abandoned children were raised in orphanages or were placed in a home while the city poor relief paid for their upbringing.
Example: Johanna Frederiks
Johanna Frederiks was the second wife of my ancestor Johan Jacob Tanto. When they got married in Enkhuizen on 23 March 1817, the record told about her:1
[...] shortly after her birth abandoned by her parents and placed by the regents of the almshouse in the poor orphanage, where she was raised by them.
- Enkhuizen, marriage record 1817 number 5, Tanto-Frederiks, 23 March 1817; “Enkhuizen,” scans, Zoekakten (http://www.zoekakten.nl : accessed 6 July 2014)