Try cleaning the faceplate and check if that resolves the problem.
Here’s a a link to the ifixit Vtech Kidizoom Smart Watch DX Faceplate Replacement guide
If that didn’t work, since you have hard reset the device then it seems as though there is a problem with the digitizer (touchscreen).
A brief search online shows no results for spare parts for the watch.
Even Vtech (click on the letter ‘K” then on Kidizoom SmartWatch) offers a USB cable as the only replacement part for the watch.
You may be able to source a “donor” watch - example only (for parts or a direct replacement of the watch) if the price is right. Something to consider perhaps.