Looking at your mapping screen now it seems that these child items are present within the mapping screen.
They just have different SKUs from what you have mentioned.
The SKUs are TH001-RD, TH001-SA and TH001-TQ and they are mapped to your Linnworks inventory.
Let us know should there still be an issue.
Have a nice day!
I have Magento 2.2.2 installed.
I am unable to download Child Variation SKUs for Configurable product. For e.g. Parent SKU is TH001 which is a configurable product. It has 3 variations (child) SKUs - TH001G, TH001R and TH001B.
LW is only able to download TH001 but neither of TH001G, TH001R or TH001B.
Unless correct mapping happens for Child SKUs, I cannot use LW for integrating with Magento 2.