New tax key parcel numbers are assigned by the Kenosha County Land Information Office. They are typically issued and available 2-3 weeks after the land division document (typically a certified survey map or subdivision plat) has been recorded with the Register of Deeds Office.
To learn what the new child parcel numbers will be, you can monitor the original parent parcel number on the Kenosha County Property Inquiry website. This database is updated nightly, so checking the database once a day will suffice. For step-by-step instructions on how to monitor the Property Inquiry database, see this handout.