It actually might be possible with some custom code, I'm not sure.
For this to work, you will have to use the Index table engine:
1. Copy this code to the functions.php file in your theme directory (copy from line 3):
2. Create a new index table on the index table settings page: https://i.imgur.com/cjhnsVw.png
This may take 10-15 minutes to complete.
3. Make sure to choose the index table engine on the search instance options: https://i.imgur.com/BowquyX.png
The code will add the child SKUs to the indexed content, so searching for the child SKU may give results. I'm not sure if this will work, but worth trying.Best,
If you like my products, don't forget to rate them on codecanyon :)