Yes, you can enable the Canvas Resize functionality for the Child Products as well. Here is how you can do it.
Backend Configurations
Firstly, a predefined size shall be created and for that navigate to Product Designer > Manage Predefined Sizes. You will get the list of created predefined sizes.
Refer to this Article to create a predefined size.
While creating the predefined size in the Product section, select the child product you want to assign to this particular predefined size.
Also, Make sure to configure the Canvas Resize at the product level.
After, all the configurations Save the settings.
